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Chapter 9

Contents

CHAPTER IX

Heat Casualty

Ludwig M. Eichna, M.D.

The global nature of World War II required men to live, work, and fight in climatic extremes far in excess of any to which most of them had ever before been exposed.1 This was particularly true of the hot climates, and troops were stationed in many of the hottest regions on earth. Lay opinion had long maintained the traditional belief that the white men could not endure very hot climates. The natives of these areas were believed to have gained, over the centuries, special adaptations to life in such environmental extremes. It was said of certain hot regions that their climate, and endemic diseases, proved a more dangerous adversary than the enemy. How did the soldier fare and perform in such hot climates? The answer is: "Well-after he had learned several fundamental rules."

The experience of the military forces in hot climates, and the lessons learned, can be briefly summarized. When troops first entered a hot region, regardless of whether it was in the United States or overseas-in the arid desert or the humid jungle-a considerable number of heat casualties were encountered. Accumulation of knowledge and experience led to effective preventive measures, so that the problem of heat casualty was greatly reduced. In the last years of the war, it was concluded that, although environmental heat constituted an added handicap to troops, hot climates were well tolerated and did not prevent effective military operations. Military experience demonstrated, from the physiological standpoint, that hot climates are not the exclusive domain of their natives and that the white man, once he has learned, can live healthfully and work efficiently in extreme heat.

ENVIRONMENTAL TEMPERATURE

Although a discussion of the environmental features of the hot climates cannot be undertaken here, some data indicating the heat loads imposed upon troops by the climates of representative hot areas will be presented. Adequate climatic data are scarce, and the only systematic meteorological data were collected by the Army Air Forces. Other reports, in which air

1The discussion in this chapter deals solely with those effects of heat as a physical agent imposing a thermal load which man must dissipate. His inability to maintain the required compensatory adjustments leads to systemic changes which render him a casualty, hereafter termed "heat casualty," "casualty from heat," "ill effects of heat," "heat disability," or "adverse effects of heat."


196

temperature is mentioned secondarily, present data obtained under many varying conditions and usually only the highest readings are recorded. As a rule, the dry bulb temperatures2 were obtained, and the more important wet bulb temperatures or dewpoint readings are lacking. With these limitations, table 39 indicates the climatic conditions for representative hot areas occupied by U.S. troops.

TABLE 39.-Climatic conditions in representative hot areas where U.S. troops were stationed

Area

Air (dry bulb)
temperatures

Approximate
relative humidity1

 

F.

Percent

Desert:

 

 

    

Southwestern United States

110-122

10-15

    

Iran

112-126

10-15

Semidesert:

 

 

    

India (dry monsoon)

98-118

20-30

Tropical:

 

 

    

Burma

98-110

50-65

    

Southwest Pacific Islands

93-112

50-65

Semitropical:

 

 

    

Southeastern United States

93-108

35-50


1Estimated representative humidity during hot season in each area. At peak dry bulb temperatures, humidities are often lower.

These temperatures give only a partial picture. They are based on observations made near fixed installations usually constructed in clearings and often near the seacoast with its moderating winds. Few data are available from areas deep within the jungle or the desert or from foxholes, caves, dugouts, tents, and other combat positions. Additional heat loads were also imposed upon men in closed spaces; for example in "buttoned" tanks, in truck cabs, in grounded planes, in ships and ships' holds, in storehouses, and in kitchens. The environment in such spaces may be much more rigorous than that of the outside air (table 40).3

Finally, the heat stress of an environment cannot be defined correctly by individual temperature readings without considering the duration of elevated temperatures and of humidities. Moderately high temperatures, continued throughout the day and night, subject personnel to greater physiological stresses than do much higher temperatures in the daytime, followed by relatively milder nights. The desert areas and small islands thus impose

2A thermometer in air, shielded from the sun, measures the air, "dry bulb," temperature; when the bulb of the thermometer is covered with a wetted wick and the thermometer is swung in air, a lower, "wet bulb," temperature is obtained, because of the evaporative cooling from the wick. The degree of lowering of the temperature is a function of the moisture content of the air.
3Adolph, E. F.: Tolerance to Heat. Report No. 1, Contract No. OEM-cmr 483, for Committee on Medical Research, Office of Scientific Research and Development, 1 Feb. 1945.


197

TABLE 40.-Maximal climatic conditions of installation in representative areas, by locationand closed spaces

Location

Temperature

Relative humidity

Installation

Temperature

Relative humidity

Dry
 bulb

Wet bulb

Dry bulb

Wet bulb

 

F.

F.

Percent

 

F.

F.

Percent

Iran

120

---

---

Tent

137

---

---

Louisiana

97

76.5

---

Buttoned tank after 4-hour run

123

91

---

Philippine Islands:

 

 

 

 

 

 

 

    

Luzon

91

79

59

Turret of stationary buttoned tank

98

93

84

         

Do

88

80

70

Loaded transport plane before takeoff

97

88

70

    

Offshore

90

80

65

Tank deck (landing ship, tank)

109

90

48


Source: (1) Data for Iran and its installation: History of Medical Section, U.S. Army Forces in the Middle East, September 1941 to September 1945. [Official record.]
(2) Data for other locations and installations: Personal observations of the author, 1944 and 1945.

a somewhat lesser heat stress and inland tropical areas a greater stress than their peak temperatures would indicate.

INCIDENCE

The incidence of heat casualty in World War II is not accurately determinable, for the following reasons: (1) The confusion regarding diagnosis, largely because medical officers were not familiar with the ill effects of heat; (2) the coexistence of other conditions, particularly wounds and injuries on which attention was focused primarily; and (3) the difficulties of recordkeeping on a global scale. With these shortcomings in mind, tables 41, 42, 43, and 44 present statistics on heat casualty in the U.S. Army in World War II.4 The data include admissions for heatstroke, heat exhaustion, and certain other ill effects of heat during 1942-44.

Tables 41, 42, and 43 indicate that, in terms of admission rates per 1,000 average strength per year, heat casualty never became a major medical problem for the Army at any time during the war. Thus, for the total Army, the admissions per 1,000 average strength per year were as follows: For 1942, 2.03; for 1943, 2.54; and for 1944, 0.88. These data are to be compared with the peacetime (1940) rates of 0.5 for the Army in the United States, 1.4 for the Army in Panama, and 1.3 for the Army in the Philippines. The wartime increase in the admission rates for heat

4Unless otherwise indicated, the statistical analysis of the ill effects of heat in the U.S. Army in World War II is based on data compiled by the Medical Statistics Division, Office of The Surgeon General, Department of the Army.


198

TABLE 41.-Admissions for ill effects of heat (excluding sunburn and burns), in the U.S. Army, by area and month, 1942

[Rate expressed as number of admissions per annum per 1,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Area

Total number 
of 
admis-
sions

Rate

Total


Jan-
uary

Feb-
ruary

March

April

May

June

July

August

Septe-
mber

Octo-
ber

Nove-
mber

Dece-
mber

Continental United States

5,852

2.20

0.03

0.01

0.10

0.27

1.30

4.13

12.49

5.80

2.29

0.25

0.06

0.03

Overseas:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

Europe

4

0.05

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.40

0.00

0.00

0.00

0.00

    

Mediterranean1

2

.09

(2)

(2)

(2)

(2)

(2)

(2)

(2)

(2)

(2)

(2)

.00

.13

    

Middle East

35

5.78

(2)

(2)

(2)

(2)

(2)

22.22

9.52

15.02

15.45

4.66

4.58

.94

    

China-Burma-India

92

10.52

(2)

(2)

7.55

.00

10.97

70.80

42.86

8.71

1.77

2.66

.00

.00

    

Southwest Pacific

122

1.72

6.38

3.64

2.95

.24

.17

.44

.13

.83

.97

1.62

2.52

5.85

    

Central and South Pacific

174

1.15

.43

.85

3.41

1.60

.88

1.49

.75

.66

.62

.40

1.09

2.23

    

North America3

8

.08

.00

.00

.00

.00

.00

.00

.72

.09

.00

.00

.00

.00

    

Latin America

114

1.12

.99

1.60

2.03

1.54

.86

.58

.75

.43

1.60

1.16

.96

1.18


          Total overseas4

727

1.24

0.94

1.55

2.34

0.95

3.92

1.64

1.15

0.70

0.85

0.59

0.72

1.33


          Total Army

6,579

2.03

0.13

0.20

0.40

0.38

1.74

3.69

10.32

4.78

2.00

0.31

0.20

0.28


1Includes North Africa.
2Few or no troops in area.
3Includes Alaska and Iceland.
4Includes admissions (176) on transports.
NOTE.-The 0.00 indicates a rate of less than 0.005.


199

TABLE 42.-Admissions for ill effects of heat (excluding sunburn and burns), in the U.S. Army, by area and month, 19431

[Rate expressed as number of admissions per annum per 1,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Area

Total number 
of 
admis-
sions

Rate

Total


Jan-
uary

Feb-
ruary

March

April

May

June

July

August

Septe-
mber

Octo-
ber

Nove-
mber

Dece-
mber

Continental United States

14,470

2.79

0.05

0.10

0.07

0.41

1.75

7.28

11.15

8.92

1.83

0.16

0.01

0.06

Overseas:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

Europe

8

0.03

0.00

0.00

0.00

0.00

0.00

0.00

0.11

0.14

0.08

0.00

0.02

0.00

    

Mediterranean2

713

1.56

0.05

.00

.00

.41

1.67

3.63

5.84

3.42

1.95

.06

.00

.02

    

Middle East

1,103

20.80

.73

.00

1.43

1.15

15.41

17.30

57.45

88.59

21.91

2.40

.00

.00

    

China-Burma-India

92

2.32

.00

.66

1.08

.44

8.91

6.56

6.18

1.57

4.80

.62

.50

.00

    

Southwest Pacific

386

2.03

3.36

3.59

2.69

1.57

1.02

.50

.93

1.28

1.20

2.75

2.58

3.04

    

Central and South Pacific

460

1.58

2.80

3.25

1.46

1.31

1.23

.26

1.00

.68

3.07

1.37

1.48

1.55

    

North America3

4

.02

.00

.00

.00

.00

.00

.00

.15

.00

.00

.00

.00

.00

    

Latin America

97

.80

1.48

82

1.13

.69

.37

.60

1.06

.96

.50

1.02

.52

.34


          Total overseas4

2,934

1.74

1.13

1.29

0.77

0.65

1.76

2.06

4.45

4.61

2.07

0.72

0.61

0.61


          Total Army

17,404

2.54

0.26

0.33

0.20

0.46

1.76

6.12

9.52

7.82

1.89

0.32

0.19

0.24


1Excludes 4 admissions characterized as battle injuries, for which the monthly distribution is not available.
2Includes North Africa.
3Includes Alaska and Iceland.
4Includes admissions (71) on transports.
NOTE.-The 0.00 indicates a rate of less than 0.005.


200

TABLE 43.-Admissions for ill effects of heat (excluding sunburn and burns), in the U.S. Army, by area and month, 19441

[Rate expressed as number of admissions per annum per 1,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Area

Total number 
of 
admis-
sions

Rate

Total


Jan-
uary

Feb-
ruary

March

April

May

June

July

August

Septe-
mber

Octo-
ber

Nove-
mber

Dece-
mber

Continental United States

4,299

1.08

0.01

0.05

0.06

0.14

1.04

3.58

3.82

2.84

1.27

0.05

0.01

0.00

Overseas:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

Europe

75

0.04

0.00

0.00

0.05

0.05

0.12

0.00

0.11

0.19

0.03

0.00

0.00

0.00

    

Mediterranean2

196

.30

.02

.06

.06

.07

.23

.64

1.19

.97

.04

.11

.00

.00

    

Middle East

158

3.41

1.20

.26

.00

1.37

3.02

15.76

14.37

4.87

.27

.49

.00

.00

    

China-Burma-India

525

3.11

.00

.00

.40

2.77

13.31

13.21

3.57

2.79

.67

.28

.17

.15

    

Southwest Pacific

1,061

1.97

3.21

2.59

2.49

1.97

2.40

2.17

1.03

1.08

1.28

3.54

1.99

1.01

    

Central and South Pacific

391

.89

1.48

.73

.89

.59

.74

1.64

1.05

.70

.71

.68

.75

.80

    

North America3

4

.03

.00

.00

.00

.00

.00

.28

.10

.00

.00

.00

.00

.00

    

Latin America

31

.36

.72

.53

.37

.13

.13

.72

.14

.15

.62

.60

.00

.15


          Total overseas4

2,535

0.67

0.66

0.53

0.52

0.52

1.19

1.45

0.89

0.71

0.35

0.66

0.40

0.25


          Total Army

6,834

0.88

0.24

0.24

0.25

0.31

1.11

2.55

2.36

1.75

0.78

0.39

0.23

0.15


1Excludes 107 admissions characterized as battle injuries, for which the monthly distribution is not available.
2Includes North Africa.
3Includes Alaska and Iceland.
4Includes admissions (94) on transports.
NOTE.-The 0.00 indicates a rate of less than 0.005.


201

TABLE 44.-Summary of heat casualties in the United States, by area, installation, and unit, 1942-43

Area and installation

Unit

Date

Heat casualties

Remarks

Total number

Number hospi-
talized

Number of deaths

Southeastern United States.1

Fourth Service Command.

1 Jan.-26 Aug. 1942.

1,307

378

13

Data compiled from 21 stations (see table 48).

Fort Eustis, Va.2 

Station Hospital.

1942

---

49

---

Fifth in frequency of hospital admissions.

Fort Eustis, Va.3

...do...

Summer of 1943.

273

---

2

Major medical problem in the summer.

Camp McCain, Miss.4

87th Infantry Division.

July and August 1943.

---

164

3

 

Camp Van Dorn, Miss.5

99th Infantry Division.

6 Apr.-11 Sept. 1943.

300

---

2

 

Desert Training Center, southern California.6

77th Infantry Division.

1943

649

183

---

 

Desert Training Center, southern California.7

...do...

8 Apr.-23 Sept. 1943.

409

25

---

 

Desert Training Center, southern California.7

...do...

8 and 9 June 1943.

73

---

---

Fell out during marching in heat.

Desert Training Center, southern California7

...do...

26-29 June 1943.

68

---

---

Strict water discipline.

Desert Training Center, Indio, California.8

7th Armored Division.

26 June-15 July 1943.

51

44

---

On maneuvers for 20 days.


1Letter, Headquarters, Fourth Service Command, to The Surgeon General, 26 Aug. 1942, subject: Report of Cases of Heat Stroke and Heat Exhaustion.
2Annual Report, Station Hospital, Fort Eustis, Va., for 1942.
3Annual Report, Station Hospital, Fort Eustis, Va., for 1943.
4Annual Report, 87th Infantry Division, for 1943.
5Annual Report, 99th Infantry Division, for 1943.
6Letter, Office of the Division Surgeon, Headquarters, 77th Infantry Division, to Commanding General, 77th Infantry Division, 3 Aug. 1943, subject: Summary of Medical Experiences and Problems on Desert Maneuvers.
7Sneidman, G. I.: Exhaustion and High Temperatures as Experienced in Desert Operations. [Professional paper.]
8Annual Report, 7th Armored Division, for 1943.


202

TABLE 45.-Deaths due to environmental heat, in the U.S. Army, by area and cause of death, 1942-45

[Rate expressed as number of deaths per annum per 100,000 average strength]
[Preliminary data based on complete files of individual medical records]

Area and cause of death

1942-45

1942

1943


1944

1945

Number of deaths

Rate

Number of deaths

Rate

Number of deaths

Rate

Number of deaths

Rate

Number of deaths

Rate

Continental United States:

 

 

 

 

 

 

 

 

 

 

    

Heatstroke

153

1.04

46

1.73

82

1.58

15

0.38

10

0.34

    

Heat exhaustion

25

.17

6

.23

12

.23

7

.18

---

0

    

Other

24

.16

6

.22

17

.33

1

.02

---

0


Total

202

1.37

58

2.18

111

2.14

23

0.58

10

0.34

Overseas:

 

 

 

 

 

 

 

 

 

 

    

Heatstroke

17

0.16

1

0.17

7

0.41

16

0.16

3

0.06

    

Heat exhaustion

11

.10

---

0

3

.18

5

.13

3

.07

    

Sunburn

1

.01

---

0

---

0

1

.03

---

0

    

Other

8

.08

2

.34

4

.24

2

.05

---

0


Total

37

0.35

3

0.51

14

0.83

114

0.37

6

0.13

Combined continental United States and overseas:

 

 

 

 

 

 

 

 

 

 

    

Heatstroke

170

0.67

47

1.45

89

1.29

21

0.27

13

0.17

    

Heat exhaustion

36

.14

6

.18

15

.22

12

.15

3

.04

    

Sunburn

1

2.00

---

0

---

0

1

.01

---

0

    

Other

32

.13

8

.25

21

.31

3

.04

---

0


Grand total

239

0.94

61

1.88

125

1.82

37

0.47

16

0.21


1Includes one death among transport admissions.
2Indicates a rate of more than zero but less than 0.005.

casualty, which occurred chiefly in the first 2 years of the war, was obviously not great. Nevertheless, because of the large number of men mobilized, the relatively low admission rates represent sizable numbers of patients, as follows: In 1942, 6,579 heat casualties with 61 deaths; in 1943, 17,404 heat casualties with 125 deaths; in 1944, 6,834 casualties with 37 deaths; and in 1945, 4,470 heat casualties with 16 deaths (tables 41, 42, 43, and 45). The study made by the Army Institute of Pathology, Washington, D.C., of the necropsy material from 125 of the 190 fatal cases of heatstroke which occurred in troops in the United States during the summer months of the 4-year period 1941 to 1944, inclusive,5 is believed to be the largest series of fatal heatstroke analyzed.

5Malamud, N., Haymaker, W., and Custer, R. P.: Heat Stroke, A Clinico-Pathologic Study of 125 Fatal Cases. Mil. Surgeon 99: 397-449, November 1946.


203

Hospital admission rates are inadequate indexes of the extent of the problem, for they indicate only the outright heat casualties. In all hot regions, there were many men who were not sufficiently incapacitated to report to sick call and who were confined to quarters or "stuck it out," working inefficiently or not at all. These men were, in truth, heat casualties to the effectiveness of the Army; but most of them were never placed on sick lists and their numbers are unknown.

Moreover, since heat casualty has a seasonal incidence, an analysis which averages the low incidence of the cool months with the high incidence of the hot months does not fully present the problem. Thus, the yearly admission rate for an area may be low, but in the hot months heat casualty may be a serious problem to a particular command. In the same manner, data averaged for large areas do not represent the problem in the component commands within the large area. The urgency and magnitude of heat casualty in individual units, for example, the Desert Training Center in southern California, may be serious and yet be completely masked when averaged with the low incidence in the cooler components of the theater, such as the northern United States. Therefore, the average yearly rates will require revision if the true significance of the ill effects of heat is to be appreciated in the units affected. An analysis of heat casualty by area and month is recorded in tables 41, 42, and 43.

Heat casualties assumed significant proportions in the Army in only three areas: The China-Burma-India theater, the Middle East theater, and the United States. High rates were temporary and largely limited to the period immediately after arrival in the areas. In the China-Burma-India theater, casualties for 1942 reached 10.52 per 1,000 per year, with a peak incidence of 70.80 per 1,000 per year for the month of June (table 41). Although heat casualty threatened to become a serious problem, the comparatively small number of troops in the theater at this time resulted in 92 admissions with 2 deaths. In the next 2 years, the incidence by month, and for the year, was decidedly lower, and heat casualty no longer constituted a significant medical problem in this theater.

In the Middle East theater, owing almost entirely to the high incidence in the Persian Gulf Command6 (table 46), heat casualty in 1943 reached 20.80 per 1,000 per year with 1,103 admissions for the year (table 42). In the summer months of July and August 1943, when the rates reached 57.45 and 88.59 per 1,000 per year, respectively, heat casualty became a major medical problem. A striking decrease occurred in the following year (table 43), when the yearly incidence fell to 3.41 per 1,000, the peak (June) incidence to 15.76 per 1,000, and total admissions to 158.

In the United States, heat casualty presented a somewhat different problem. The admission rates per 1,000 per year were always relatively low (2.20, 2.79, and 1.08 for 1942, 1943, and 1944, respectively), but be-

6Annual Report, U.S. Army Forces in the Middle East, for 1943.


204

TABLE 46.-Incidence of heat casualty in U.S. Army Forces in Middle East, by area or command, from 1 July 1942 to 1 October 1943

[Incidence expressed as number of heat casualties admitted to hospital or quarters or both]

Area or command

Heat exhaustion

Heatstroke

Sunburn

Miscellaneous

Total

Eritrea

50

---

1

49

100

Libya

8

---

2

---

10

Delta

6

1

6

5

18

Levant

2

---

1

---

3

Headquarters, USAFIME

---

---

---

---

---

Air Force

20

---

4

---

24

Persian Gulf

1,070

16

10

92

1,188

West Africa

---

---

1

---

1


Total

1,156

17

25

146

1,344


Source: Annual Report, U.S. Army Forces in the Middle East, for 1943.

cause of the large number of men in training, the total number of patients exceeded that of all other theaters combined (tables 41, 42, 43, 47, and 48). In 1942, there were 5,852 cases with 58 deaths; in 1943, 14,470 cases with 111 deaths; and in 1944, 4,299 cases with 23 deaths.7 These data are for the whole of the United States, whereas the heat casualties occurred in camps in the Southern States. It is of interest that the largest number of casualties and deaths due to heat occurred in troops in the United States where the climate, even in the southeast and southwest, is not ordinarily considered hot when compared with the climate of India, Burma, or Iran.

Since overall statistics tend to minimize the problems encountered by individual units placed in climatic extremes, it seems appropriate to list some of the more serious experiences with heat casualty sustained by different units in the United States (see table 44).

The illustrations given in table 44 were chosen from units reporting high casualty rates. Other units in the same areas did not mention heat casualty. This may have been an omission or such units may have profited by the example of their predecessors and neighbors and instituted measures which reduced heat casualty to such a minor role that it was not deemed worthy of note. Nevertheless, heat casualties were still frequent in troops in the United States (tables 43 and 45), and a survey from 1 to 31 August 1944 revealed 18 stations reporting 6 or more cases during this period (table 49).

Illustrative examples from oversea theaters are more difficult to obtain. In the Middle East, casualty from heat accounted for 11.7 percent of hospital admissions in the Persian Gulf Command, from 6 June to 9 December 1942, and was exceeded in importance only by enteritis (28 percent) and

7In 1945, there were 2,315 admissions with 10 deaths.


205

TABLE 47.-Admissions and deaths for heat casualties among troops in the United States, by month and year, January-December, 1942, 1943, and 1944

[Rate for admissions expressed as number of admissions per annum per 1,000 average strength]
[Rate for deaths expressed as number of deaths per annum per 100,000 average strength]
[Preliminary data based on sample tabulations of individual medical records]

Month

1942

1943

1944


Number

Rate

Number

Rate

Number

Rate

 

Admissions1

January

4

0.03

20

0.05

4

0.01

February

2

.01

40

.10

18

.05

March

16

.10

30

.07

23

.06

April

47

.27

180

.41

53

.14

May

248

1.30

805

1.75

370

1.04

June

822

4.13

3,250

7.28

1,200

3.58

July

2,693

12.49

5,165

11.15

1,296

3.82

August

1,352

5.80

4,080

8.92

932

2.84

September

569

2.29

800

1.83

386

1.27

October

70

.25

70

.16

13

.05

November

18

.06

5

.01

4

.01

December

11

.03

25

.06

---

0


Total

5,852

2.20

14,470

2.79

4,299

1.08

 

Deaths2

January

---

0.00

---

0.0

---

0.0

February

---

0

---

0

---

0

March

---

0

---

0

---

0

April

---

0

---

0

---

0

May

1

.52

4

.87

1

.28

June

3

1.51

18

4.03

5

1.49

July

32

14.85

63

13.60

4

1.18

August

15

6.43

26

5.68

8

2.44

September

7

2.82

---

0

5

1.64

October

---

0

---

0

---

0

November

---

0

---

0

---

0

December

---

0

---

0

---

0

Total

58

2.18

111

2.14

23

0.58


1There were 2,315 admissions in 1945.
2There were 10 deaths in 1945.


206

TABLE 48.-Heat casualties in Fourth Service Command, by station, 1 January-26 August 1942

Station

Heat casualties

Total number

Number hospitalized

Number of deaths

Fort Barrancas, Fla.

6

6

---

Fort Benning, Ga.

15

15

1

Camp Blanding, Fla.

8

8

---

Fort Bragg, N.C.

107

107

5

Camp Croft, S.C.

86

86

1

Camp Davis, N.C.

12

12

---

Camp Forrest, Tenn.

---

---

---

Camp Gordon, Ga.

9

4

---

Fort Jackson, S.C.

31

31

---

Key West Barracks, Fla.

1

1

---

Fort McClellan, Ala.

511

(1)

2

Fort McPherson, Ga.

---

---

---

Fort Moultrie, S.C.

1

1

---

Fort Oglethorpe, Ga.

6

6

---

Camp Rucker, Ala.

28

28

---

Fort Screven, Ga.

---

---

---

Camp Shelby, Miss.

5

---

---

Camp Stewart, Ga.

11

11

---

Camp Sutton, N.C.

26

26

---

Camp Tyson, Tenn.

1

1

---

Camp Wheeler, Ga.

443

35

4

Total

1,307

378

13


1Statistics were not furnished.

venereal disease (12 percent).8 In the same theater from 1 July 1942 to 1 October 1943, 1,344 heat casualties represented 2.5 percent of all admissions.

The 113th General Hospital arrived at Ahvāz, Iran, on 28 May 1943 and by the end of the year had treated 8 cases of heatstroke, 221 cases of heat exhaustion, and 124 cases of ill-defined effects of heat; a total of 353.9 Apart from the Persian Gulf Command, heat casualties in other parts of the Middle East in 1942 and 1943 were few, except for Eritrea, where 99 cases occurred during the period from 1 July 1942 to 1 October 1943 (table 46).

Most reports from the Central and South Pacific and the Southwest Pacific do not mention heat casualty, or pass over it in general terms. There are some exceptions. The annual report for 1942 of the Office of the Surgeon,

8History of Medical Section, U.S. Army Forces in the Middle East, September 1941 to September 1945. [Official record.]
9Annual Report, 113th General Hospital, for 1943.


207

TABLE 49.-Stations in the United States reporting six or more casualties from ill effects of heat between 1 and 31 August 1944

[Rate expressed as number of admissions per annum per 1,000 average strength]

Service Command

Station

Strength

Heat casualties

Number

Rate

First

Fort Devens, Mass.

13,500

8

7

Third

Aberdeen Proving Ground, Md.

24,782

9

4

    

Do...

Fort Lee, Va.

34,653

6

2

Fourth

Fort Benning, Ga.

71,447

25

4

    

Do...

Camp Blanding, Fla.

56,049

60

13

    

Do...

Camp Croft, S.C.

20,195

8

5

    

Do...

Camp Rucker, Ala.

30,057

15

6

    

Do...

Camp Van Dorn, Miss.

33,170

8

3

Fifth

Camp Breckinridge, Ky.

35,249

9

3

    

Do...

Fort Knox, Ky.

34,625

6

2

Seventh

Fort Riley, Kans.

29,897

13

5

Eighth

Camp Barkeley, Tex.

44,516

25

7

    

Do...

Camp Chaffee, Ark.

27,665

17

7

    

Do...

Camp Claiborne, La.

49,208

11

3

    

Do...

Fort Hood, Tex.

60,869

77

15

    

Do...

Camp Joseph T. Robinson, Ark.

38,501

35

11

    

Do...

Camp Maxey, Tex.

31,796

15

6

Ninth

Camp Roberts, Calif.

33,176

26

9


U.S. Army Forces in the South Pacific Area, in referring to the activities on Guadalcanal states: "The major medical problems were battle casualties, malaria, dysentery, tropical ulcers, and heat exhaustion."10 In a report dated 20 February 1943, the surgeon of the 101st Medical Regiment, attached to the Americal Division, considered heat exhaustion a medical problem which in order of frequency of medical admissions stood 10th, with 141 admissions up to 14 February 1943, as compared to 3,102 admissions for malaria (first in the cause of medical admission) over the same period.11 The leading medical causes for admission to three field hospitals of the 101st Medical Regiment were as follows:

Cause

Number of cases

Malaria (all types)

3,102

Nervous disorders

483

Enteritis

416

Cellulitis

411

Fever of unknown origin

343

Upper respiratory infection

302

Jaundice

248

Skin disease

234

Otitis media

227

Heat exhaustion

141


10Annual Report, U.S. Army Forces in the South Pacific Area, for 1942.
11Annual Report, 101st Medical Regiment for 1942, with enclosure 8 thereto, dated 20 Feb. 1943.


208

In the 25th Infantry Division during operations on Guadalcanal, New Guinea, and Morotai (1943 and 1944), heat exhaustion caused from 5 to 10 percent of all medical casualties and occurred chiefly in troops on the offensive or on forced marches.12 For the 41st Infantry Division, the following was noted:

Especially in the Hollandia operation and the present Biak landing, heat exhaustion cases have been third in the cause of hospital admission. Experience has also shown diminution of combat efficiency in many more personnel who were not prostrated to the extent of requiring hospitalization.13

In the China-Burma-India theater, the hot humid climate led to lethargy and decreased efficiency of work, but frank heat casualty was infrequently encountered after 1942. Even so, in Gaya, India, during June 1945, when the air temperature reached 113 F., eight cases of heat exhaustion were treated at the 99th Station Hospital, with one death.14 The islands in the Pacific Ocean Area do not, for the most part, have hot climates, and the reports do not list heat as a cause of casualty there. Similarly, reports from the Mediterranean, South Atlantic, and Caribbean Commands either fail to mention heat casualty or routinely state "no ill effects of heat," leading to the conclusion that in these areas climate can be disregarded as a detrimental factor.

In summary, heat casualty constituted a medical problem which, though by no means a major one, could not be ignored. In absolute numbers, many men became casualties because of heat, and in specific areas, at given times, the problem was serious and urgent.

Decrease in Incidence

The incidence of heat casualty in all hot theaters decreased steadily as the war progressed, until in the last year of the war it became a minor medical problem, even in the hottest areas. The experience in the Middle East theater is a striking example of this reduction. Troops moved into this theater in the last half of 1942 and the first half of 1943. The summer of 1943 found a considerable body of troops exposed to the hot desert for the first time in their lives. Heat casualties for 1943 numbered 1,103 cases with an admission rate of 20.80 per 1,000 per year and, in August, a peak monthly incidence of 88.59 per 1,000 per year (table 42). In 1944, however, the number of cases declined to 158, the yearly admission rate to 3.41 per 1,000 per year, and the peak monthly (June) incidence to 15.76 per 1,000 per year (table 43). The experience in the Persian Gulf Command set the pattern for the entire theater. This marked reduction in heat casualty was achieved, with the command breaking all records moving supplies,

12U.S. Army Forces, Far East, Board Report No. 145, Questionnaire of Armored Medical Research Laboratory on Problems of Jungle Warfare.
13Annual Report, 41st Infantry Division, for 1944 (2d quarter).
14Personal correspondence, medical officer in India, to author.


209

even though the summer of 1944 was as hot as the summer of 1943. Individual unit figures showed the same improvement.

The experience of the Persian Gulf Command is especially significant since this was the hottest theater in which troops were stationed for long periods. The final opinion of the Command was that, once it had learned and instituted proper living conditions, proper working hours, and proper handling of troops, it could maintain effective work without significant illness from the heat.

In the China-Burma-India theater, the experience was essentially the same. During the first year (1942), the admission rate was 10.52 per 1,000 per year and the peak monthly rate, 70.80 per 1,000 per year. In 1943, these rates fell to 2.32 and 8.91, respectively, and in 1944 they were 3.11 and 13.31 (tables 41, 42, and 43). The fact that the total yearly caseload increased from 92 in 1942 to 525 in 1944 was a reflection of the increased number of troops in the theater, for heat casualty was no longer considered a significant medical problem.

In the United States, heat casualties reached their maximum in 1943 and decreased thereafter. High monthly peak rates were encountered during the summers of the first 2 years, 12.49 per 1,000 per year in July of 1942 and 11.15 per 1,000 per year in July 1943, but only slightly increased yearly rates, 2.20 per 1,000 per year in 1942 and 2.79 per 1,000 per year in 1943 (tables 41 and 42). The total yearly caseload of 5,852 in 1942 increased to 14,470 in 1943, the highest figure of the war and indicative of the large number of men in training. Deaths due to heat numbered 58 in 1942 and 111 in 1943. The following year (1944), the number of cases diminished to 4,299, the admission rate fell to 1.08 per 1,000 per year, and the peakload during the summer months dropped to 3.82 per 1,000 per year (table 43). Deaths for the year numbered 23, and in 1945 with 2,315 cases, there were only 10 fatalities.

The reports from the Central and South Pacific and the Southwest Pacific theaters were instructive. Except in some of the earlier island campaigns, heat casualty was not a serious matter. Although these theaters became increasingly active in 1944 and 1945, they profited by the experiences with heat casualty in the other hot theaters in the earlier years of the war. Thus, in the Southwest Pacific Area, the admission rate remained quite uniform throughout the war, 1.72 per 1,000 per year in 1942, 2.03 per 1,000 per year in 1943, and 1.97 per 1,000 per year in 1944, while the progressively increasing number of cases-122, 386, and 1,061 for the 3 years respectively (tables 41, 42, and 43)-was again a reflection of the increase in the number of troops.

In the last years of the war, most of the reports from China-Burma-India, the Southwest Pacific Area, and even the Middle East either do not mention ill effects of heat or indicate that heat casualty was not a medical


210 

problem of significance. The general opinion was that although the efficiency of personnel was reduced there was little overt illness.

The reduction in heat casualty as the war progressed must be evaluated in terms of the progress of events in the various theaters. In some theaters, the movement of troops out of hot areas may have accounted for the reduction in heat casualty; for example, in the United States where troops were moved from training centers to oversea stations. However, similar reductions occurred in theaters where the number of troops remained unchanged while the demands on them increased; for example, in the Persian Gulf Command. Furthermore, low heat casualty rates persisted in still other theaters, such as the Southwest Pacific, which became progressively more active. These observations indicate that the reduction in heat casualties in the later years of the war was real.

These data lead to the implied conclusion that heat casualty as a major problem is preventable under all circumstances in all hot environments. However, it must be considered that in the hottest areas on earth (Persian desert, lowland India, and Burma) military activity was concerned largely with stable operations, such as supply and transportation, rather than with the less well regulated activity of combat. Most of the prolonged, large-scale combat was conducted in hot areas of somewhat lesser heat stress. Under these circumstances, it may be said that (1) relatively stable operations were carried out with diminished heat casualty in the hottest areas on earth and that (2) active large-scale combat was successfully waged in hot areas of somewhat lesser heat stress, where it was also possible to prevent a large amount of heat casualty. Since large-scale combat was not conducted in the hottest areas, it is not known whether the available preventive measures against heat casualty could have been effectively applied under such fluid and less ordered conditions.

CAUSE AND PREVENTION

The experience of the Armed Forces during World War II contains the answer to the problem of living and working in hot climates. Why were adverse effects of heat prevalent in the early years of the war? And why did they decrease toward the end of the war? It is the purpose of the remainder of this review to indicate the measures responsible for reducing heat casualty.

A consideration of the military situation at the time the United States entered the war may serve as a background. The last half of 1941 and the first half of 1942 saw much military activity in hot climates. The battles in the African desert between the British and German Armies and the march of the Japanese through the jungles of Southeast Asia and the islands of the Southwest Pacific focused attention on the advantages to be gained by operations in legions previously considered impossible for com-


211

bat because of climate. Moreover, the strength of the home fortresses of both Germany and Japan was considered so formidable that counterattack seemed most feasible from the periphery; that is, the recently conquered hot desert and jungle areas. Desert and jungle fighters were needed. However, there were many defects in our knowledge and experience of the peculiar stresses imposed by hot climates, of their deleterious effects, and of the measures required to prevent heat casualty.

The factors which led to heat casualty, and the corrective measures taken to prevent such illness, were apparently much the same in all areas regardless of their location. This suggests that the same basic factors were operating in the different areas, whether jungle or desert, and that the experiences from all areas may be combined.

Acclimatization

For some time, it has been known that man must adapt himself (acclimatize) to a hot environment before he can perform physical work in that environment effectively. The failure to appreciate the need for acclimatization led some commanding officers to require men newly arrived from temperate into hot climates to perform hard work immediately.15 Inevitably, heat casualties resulted. In some areas, they were serious and numerous; in others, relatively mild to moderate. A majority of the cases of fatal heatstroke occurring in the Army in the United States occurred in men who had been stationed in a hot environment for only a short period (a month or less).16 Moreover, most of these fatalities occurred in men who originally came from the northern part of the United States. Lack of acclimatization may also be considered an important factor in those heat casualties which occurred during a sudden rise in temperature in more temperate areas.

The need for acclimatization was quickly learned. Whenever possible, troops newly arrived in hot climates were not at first required to perform a full day's work but were handled on programs of progressively increased work until they were fully acclimatized. Heat casualties quickly decreased, and troops were able to work hard in the heat without ill effects. It was generally felt that 1 month was required to attain full acclimatization, although considerable adaptation was attained in 4 or 5 days. The need of acclimatization led to the realization that troops should be trained in climates similar to those in which they were ultimately to work or fight.

Laboratory studies on acclimatization to heat confirmed the observations in the field, clarified the physiological processes involved, and pro-

15Report, Armored Medical Research Laboratory, Fort Knox, Ky., 20 Oct. 1942, Project No. 2-8, Report on Results of Desert Field Study.
16Schickele, E.: Environment and Fatal Heat Stroke; An Analysis of 157 Cases Occurring in the Army in the U.S. During World War II. Mil. Surgeon 100: 235-256, March 1947.


212

vided a sound basis for corrective measures.17 These studies, conducted in hotrooms, revealed several pertinent facts. Hard work on first exposure to hot environments (both dry and humid) is never well tolerated and, if continued, leads to disability, no matter how excellent the general physical fitness. The unacclimatized man working in the heat manifests two major undesirable phenomena which usually incapacitate him. He retains heat, with a marked rise in body temperature, and his circulation becomes deranged and unstable. Acclimatization is the development of physiological adaptation of which the mechanism is not yet completely understood but which maintains the body's thermal balance by increasing heat loss to meet the increased heat loads. This appears to be accomplished largely by the development of increased evaporative cooling through more rapid and more copious sweating.18 In turn, the deranged, unstable circulation of the unacclimatized state, associated with the heat retention, is avoided. Acclimatization begins with the first exposure to heat and is attained most rapidly and completely by progressively increasing the amount of daily work performed in the heat to the point of comfortable tolerance. The major portion of the adaptation is attained in from 4 to 7 days and then progresses more slowly for 3 or 4 weeks. Physically fit men acclimatize more quickly than the unfit. On returning to a cool environment, acclimatization is retained well for 1 or 2 weeks after which it is lost at variable rates. In some men, it is retained to an appreciable extent for as long as 1 to 2 months. The many factors which are detrimental to the well-being and performance of men in the heat produce greater effects in unacclimatized than in acclimatized men.

Water

In the early days of the war, line officers believed in a water discipline, the two principal tenets of which were that drinking water during work in the heat is harmful and that men could be trained to work in the heat with progressively lower intakes of water. Their ideal was the "desert fighter" who could fight on "a pint of water a day." Such a man is a mythical figure,

17(1) Bean, W. B., and Eichna, L. W.: Performance in Relation to Environmental Temperature; Reactions of Normal Young Men to Simulated Desert Environment. Fed. Proc. 2: 144, 1943, (2) Eichna, L. W., Bean, W. B., Ashe, W. F., Jr., and Nelson, N.: Performance in Relation to Environmental Temperature; Reactions of Normal Young Men to Hot Humid (Simulated Jungle) Environment. Bull. Johns Hopkins Hosp. 76: 25-58, January 1945. (3) Taylor, H. L., Henschel, A. F., and Keys, A.: Cardiovascular Adjustments of Man in Rest and Work During Exposure to Dry Heat. Am. J. Physiol. 139: 583-591, August 1943. (4) Henschel, A., Taylor, H. L., and Keys, A.: The Persistence of Heat Acclimatization in Man. Am. J. Physiol. 140: 321-325, December 1943. (5) Robinson, S., Turrell, E, S., Belding, H. S., and Horvath, S. M.: Rapid Acclimatization to Work in Hot Climates. Am. J. Physiol. 140: 168-176, November 1943. (6) Machle, W.: The Physiological Effects of High Temperatures. Mil. Surgeon, 95: 98-105, August 1944. (7) Machle, W., and Hatch, T. F.: Heat: Man's Exchanges and Physiological Responses. Physiol. Rev. 27: 200-227, April 1947. (8) Taylor, C. L.: Physical Exertion in the Heat; Some Notes on Its Physiology and Hygiene. J. Aviation Med. 17: 137-145, April 1946.
18Report, Medical Department Field Research Laboratory, Fort Knox, Ky., 30 June 1947, Project No. 2-17-1, Thermal Regulation During Early Acclimatization to Work in a Hot Dry Environment.


213

but the concept played a major role in producing heat casualties, particularly in the United States, where unacclimatized and relatively unfit men were suddenly required to undergo vigorous physical exertion in hot environments with limited, and inadequate, intakes of water. Insufficient water also led to heat casualty in some of the earlier Pacific island campaigns where men went ashore to perform strenuous activities with limited water supplies which could not be augmented until the combat situation improved. Medical officers in the field considered inadequate water intake and the subsequent dehydration one of the most important factors leading to heat casualty. In numerous reports,19 they pointed out the need for an adequate intake of water based not on preconceived ideas or hopes but on the actual needs of the men as determined physiologically by their water losses.

Studies in laboratory hotrooms20 and in the field21 quickly produced data which substantiated the recommendations of the medical officers in the field and disproved completely the possibility of training men to reduce their water requirements. The huge water losses in sweat, approximately a liter per hour for men working in the desert or jungle environment, continue whether or not water is drunk and are only slightly reduced by dehydration. The sweat loss automatically sets the amount of water that must be replaced. Failure to do so leads to dehydration, with reduced blood volume, and predisposes to disability. It was repeatedly demonstrated that hardened, well-acclimatized men, who performed easily and well in the heat while drinking water as desired, either failed to complete the same amount of work or did so with great difficulty and marked inefficiency when on

19(1) Annual Report, 87th Infantry Division, for 1943. (2) Annual Report, 99th Infantry Division, for 1943. (3) Letter, Office of the Division Surgeon, Headquarters, 77th Infantry Division, to Commanding General, 77th Infantry Division, 3 Aug. 1943, subject: Summary of Medical Experiences and Problems on Desert Maneuvers. (4) Sneidman, G. I.: Exhaustion and High Temperatures as Experienced in Desert Operations. [Professional paper.] (5) Annual Report, Persian Gulf Command, for 1944. (6) Annual Report, 113th General Hospital, for 1944. (7) Report, Headquarters, XIV Corps, to Commanding General, South Pacific, 3 June 1943, subject: Informal Report on Combat Operations. (8) Annual Report, 102d infantry Division, for 1943. (9) Annual Report, 81st Infantry Division, for 1943. (10) Letter, Office of The Surgeon General, to Commanding General. Services of Supply, 28 July 1942, subject: Heat Exhaustion and Fatigue. (11) Wallace, A. W.: Heat Exhaustion. Mil. Surgeon 93: 140-146, August 1943.
20(1) See footnote 17 (1), (2), (6), (7), and (8), p. 212. (2) Pitts, G. C., Johnson, R. E., and Consolazio, F. C.: Work in the Heat as Affected by Intake of Water, Salt and Glucose. Am. J. Physiol. 142: 253-239, September 1944.
21(1) Adolph, E. F., Rahn, H., Gosselin, R. E., Goddard, D. R., Brown, A. H., Kelly, J. J., and Wolf, A. V.: Water Losses From Man in the Desert. Report No. 1, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development, 20 Mar. 1943. (2) Rothstein, A., and Brown, A. H.: Water Requirements of Air Force Personnel in the Desert During the Hot Season. Report No. 11, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research. Office of Scientific Research and Development, 15 Oct. 1943. (3) Rothstein, A., and Gosselin, R, E.: Rates of Sweat Loss in the Desert. Report No. 15, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development, 30 Jan. 1944. (4) Adolph, E. F., Brown. A. H., Siple, P. A., and Heald, W. F.: Survival Time of Men Without Water in the Desert. Report No. 8, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development, 23 May 1943. (3) Adolph, E. F., and Brown, A. H.: Economy of Drinking Water in the Desert. Report No. 5, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development, 25 May 1943. (6) Adolph, E. F.: Water Shortage in the Desert. Report No. 12, University of Rochester, Contract No, OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development. 20 Oct. 1943.


214

restricted water intakes. Furthermore, nothing is gained by failing to replace the water losses as they occur. The total 24-hour water intake was found to be just the same whether men drank as they desired, whenever thirsty, or only at stated periods, such as mealtime. Withholding water until stated drinking hours not only did not reduce the water intake but also led to dehydration, with its discomfort and potentially serious consequences.

"Thirst quenchers" were shown to be of no value.22 They neither reduced the water requirement nor alleviated discomfort. Only one sound way of reducing the amount of drinking water was found; that is, wetting the clothing with nonpotable water.23 The cooling effect of evaporation of this water reduces the sweat output and conserves body water.

Quantitative studies based on observations in the field24 and in the laboratory25 determined the water requirements for different rates of work in various types of hot climates (table 50). When troops received amounts of water adequate to meet these requirements, the incidence of heat casualty decreased sharply.26

A byproduct of the quantitative studies was the prediction of survival times in hot climates for men deprived of water and the formulation of a sound plan of action for troops caught in such a predicament:

If men are isolated and have no hope of reaching water in a few hours they should as far as is feasible minimize their rate of water loss (1) obtaining maximal protection from the sun, (2) remaining as inactive as possible, (3) using what water they may

TABLE 50.-Water requirements for representative types of work in hot climates, by type of activity

Activity

Illustrative duty

Water requirement1 in-

Moderate temperatures2 (desert or jungle)

Severe temperatures3 
(desert or jungle)

 

 

Quart

Quart

Light

Desk work; guard; kitchen police

6

10

Moderate

Routine march on level; tank operation

7

11

Heavy

Forced marches; stevedoring; entrenching

9

13


1Number of quarts calculated per man per day, for drinking purposes only.
2For desert, air temperature below 105 F.; for jungle, air temperature below 85 F.
3For desert, air temperature above 105 F.; for jungle, air temperature above 85 F.

Source: War Department Technical Bulletin (TB MED) 175, June 1945.

22Wills, J. H.: Attempted Relief of Distress in Dehydrated Men by Certain Drugs. Report No. 14, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development, 24 Dec. 1943.
23Lifson, N., and Visscher, M. B.: Effect of Wet Garments on Body Weight Loss at High Environmental Temperatures. J. Indust. Hyg. & Toxicol. 25: 434-439, December 1943.
24(1) See footnote 21 (1), (2), and (3), p. 213. (2) Adolph, E. F., and Brown, A. H.: Prediction of Water Requirements of Men in the Desert. Report No. 7, University of Rochester, Contract No. OEM-cmr 206, for Committee on Medical Research, Office of Scientific Research and Development, 25 May 1943.
25Report, Armored Medical Research Laboratory, Fort Knox, Ky., 20 May 1943, Project No. 2-6, Determination of Water and Salt Requirements for Desert Operations.
26Circular Letter No. 119, Office of The Surgeon General, Army Service Forces, 3 July 1943, subject: Acclimatization, Including Water and Salt Requirements of Troops in Hot Climates.


215

have in moderation and only after dehydration has proceeded for half a day since water is lost slightly more rapidly in early stages of dehydration than later, (4) confining any necessary exertion (walking toward water) to the cooler hours of the night, (5) seeing that no water they already have is spilled or wasted.27

Since men are unable to walk after losing body water to the extent of 10 percent of their body weight, but may survive if rescued when they have lost body water to the extent of 20 percent of their body weight, the following survival times at stated activity have been calculated: (1) At daily mean shade temperature below 70 F., 3 nights of walking can be accomplished (65 miles); (2) at daily mean shade temperatures between 70 and 80 F., 2 nights of walking can be completed (45 miles); and (3) with daily mean shade temperature above 80 F., a man can walk only 1 night (25 miles). Also, if the mean temperature is 95 F., a man reaches the limit of his walking ability in 1 day, and at 120 F., in one-third of a day. The importance of limiting activity to the cooler hours of the night, when the water losses through sweating are somewhat diminished, at once becomes apparent.

The importance of an adequate water intake in the prevention of heat casualty cannot be overstressed. Since it is physiologically impossible to reduce the water losses in a hot environment, such losses must be replaced.

Salt

The need for an adequate salt intake to replace the salt lost through sweating seems to have been better understood by line officers than the need for water replacement. At times, this need was overemphasized, and salt replacement was sometimes considered more important than water replacement. In some instances, the serious mistake was made by considering that the administration of added salt automatically took care of the water requirement.

Ill effects attributable solely to salt deficiency (heat cramps) were either absent, or infrequently encountered. Nevertheless, reports from hot theaters stated that inadequate salt intake played a significant part in the production of heat casualty and that casualties were salt deficient. Medical officers advocated the use of salt and noted beneficial effects as a result, not only in the reduction of heat casualty but also in the improved well-being and work efficiency of the men. Since so many reports recommended additional salt, its advantages cannot be discounted. However, one cannot overlook the fact that salt was usually taken with water and that the added water may have really been the more significant addition.

The intake of supplemental salt proved to be quite a problem. Compressed tablets of salt did not dissolve well and at times passed through the gastrointestinal tract only partially absorbed. Nausea and vomiting often resulted from their irritation of the stomach. These effects prejudiced the

27See footnote 21 (4), p. 213.


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men against salt. Of greater importance was the risk of further dehydration from loss of fluid in the vomitus and through the curtailment of oral intake of fluids. In order to reduce gastric irritation, tablets with different fillers were tried. Sodium bicarbonate and glucose tended to induce more rapid disintegration and solution of the tablet but did not remove the gastric irritation. Another approach was the use of a plastic filler to retard the rate of solution of the tablet yet permit complete solution of the salt within the insoluble plastic matrix. Perhaps the best method developed was to dissolve the salt in water to make a final concentration of 0.1 percent salt-two 10-grain salt tablets or one-fourth of a teaspoonful of salt to each quart canteen of water.25 Though brackish, such water is not unpleasant and a taste for it is quickly acquired. By the addition of colloids and flavors, such as are contained in milk and barley water for example, the orally tolerated salt content of liquids can be increased up to 0.2 to 0.4 percent. These concentrations are not often necessary. Finally, most of the salt requirement can be supplied by salting the food more heavily, particularly the bland foods, such as potatoes and rice.

Controlled studies in the laboratory29 and in the field30 proved that water replacement is much more important, and critical, than salt replacement and that deterioration in working efficiency and heat casualty will result much more quickly when water is denied than when salt is withheld. Maximum work efficiency in the heat is maintained when water is replaced hour by hour; salt, day by day. Although efficiency and output of work fall when the salt intake is inadequate, too much salt, or salt without water, produces not only distressing subjective symptoms but also requires body water for its excretion and actually leads to a reduced work efficiency.

During acclimatization to heat, the body adapts to conserve salt by secreting a sweat low in salt content. This compensating mechanism of the sweat glands is very effective. When salt intake is reduced sharply, the salt concentration in sweat becomes very low, permitting equilibrium on intakes as low as 3 grams daily even though the daily sweat output is from 6 to 8 liters.31 The adrenal gland is suggested as the mediator of this mechanism.32

28See footnotes 25 and 26, p. 214.
29(1) See footnote 20 (2), p. 213. (2) Taylor, H. L., Henschel, A., Mickelsen, O., and Keys, K.: The Effect of Sodium Chloride Intake on the Work Performance of Man During Exposure to Dry Heat and Experimental Heat Exhaustion. Am. J. Physiol. 140: 439-451, December 1943. (3) Johnson, R. E., Belding, H. S., Consolazio, F. C., and Pitts, G. C.: The Requirements of Water and of Sodium Chloride for the Best Performance of Men Working in Hot Climates. Report No. 13, Harvard Fatigue Laboratory, for the Committee on Medical Research, Office of Scientific Research and Development, 25 Sept. 1942.
30(1) See footnote 21 (3), p. 213. (2) Adolph, E. F., Wolf, A. V., and Kelly, J. J.: Salt in Relation to Water Metabolism in the Desert. Report No. 3, University of Rochester, Contract No. OEM-cmr 206, for the Committee on Medical Research, Office of Scientific Research and Development, March 1943.
31(1) Conn, J. W., and Johnston, M. W.: Improvement of Ability of Soldier to Work in Humid Heat. Report No. 18, Contract No. OEM-cmr 232, for the Committee on Medical Research, Office of Scientific Research and Development, 1 Mar. 1944. (2) Conn, J. W., and Johnston, M. W.: Improvement of Ability of Soldier to Work in Humid Heat. Report No. 10, Contract No. OEM-cmr 232, for the Committee on Medical Research, Office of Scientific Research and Development, 1 July 1944.
32Conn, J. W., and Johnston, M. W.: Improvement in Ability of Soldier to Work in Humid Heat. Report No. 18, Contract No. OEM-cmr 232, for the Committee on Medical Research, Office of Scientific Research and Development, November 1945.


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As stated on page 212, sweat output increases during acclimatization to heat. Because salt conserving mechanisms exist but water conserving mechanisms do not, replacement of the salt is physiologically less urgent than replacement of the water. Determinations of the chlorides in the blood and the urine of troops in the American desert area33 and in the urine of troops on several of the Pacific islands34 revealed no salt deficits in the men even after long sojourns in the hot climates.

Activity

Most heat casualties occurred during, or shortly after completion of, strenuous physical activity, such as long or forced marches often with heavy packs, close order drill, obstacle course runs, and various types of field exercises. Resting or lightly active men were rarely affected. Thus, of the 265 heat casualties treated by the Station Hospital, Fort Eustis, Va., from 1 May 1943 through September 1943, none occurred on Sunday.35

Physical activity as a causative factor in heat casualty was closely associated with the external temperature. Work which could be performed without difficulty in the cooler parts of the day led to heat casualty when attempted in the midday hours. In all hot areas, medical officers quickly recommended decreased physical activity during the heat of the day. Schedules were revised and, where possible, the midday siesta became a part of the daily routine, even to being enforced in some areas. The early morning hours and the nights were utilized for work, and heat casualty diminished; often, work output increased and morale improved. For example, in the summer of 1944, the Persian Gulf Command instituted daily rest periods from 1300 hours to 1700 hours, during which vehicles were not driven across the desert, except in emergencies. Records for the hauling of supplies were broken in July of that year (p. 208). Even in combat, military observers recommended that H-hour be as early as possible for "during the middle of the day the heat is so intense that troops make little progress."36

After correlating the incidence of heat casualty in troops in training with observed environmental temperatures, medical officers recommended that physical activity should be reduced when the environmental wet bulb temperature reached 70 F. and that it should be halted for unseasoned

33Rosenbaum, L.: Significance of Salt (NaCl) in Torrid Temperatures. Mil. Surgeon 98: 43-47, January 1946.
34(1) Report, Special Survey Team, to The Surgeon General, 22 Aug. 1945, subject: Nutrition Survey in Pacific Theater of Operations. (2) Kark, R. M., Aiton, H. F., Pease, E. D., Bean, W. B., Henderson, C. R., Johnson, R. E., and Richardson, L. M.: Tropical Deterioration and Nutrition. Clinical and Biochemical Observations on Troops. Medicine 26: 1-40, February 1947.
35Borden, D. L., Waddill, J. F., Grier, G. S. III: Statistical Study of 265 Cases of Heat Disease. J.A.M.A. 128: 1200-1205, 25 Aug. 1945.
36Report, to Commanding General, Army Forces, Army War College, 11 July 1944, subject: Observer Report on the Marianas Operation (FORAGER).


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troops when it reached 81 F.37 When activity in the midday heat could not be discontinued, men were to be trained by gradually increasing their activity during the hot hours,38 and the loads at these hours were to be as light as possible.

Removing the men from the midday sun also served to prevent incapacitating sunburn. The harmful effects of solar actinic rays and the need for gradually increasing exposure in order to avoid disabling sunburn had to be emphasized.

The relation between the maximum rate of efficient work possible and the severity of environmental heat and humidity received considerable controlled laboratory study during the war.39 The problem proved to be complex, and its full consideration is beyond the scope of this review. However, when the severity of the environment increased, the work rate possible without ill effects always decreased. The simplest index of the severity of an environment for work proved to be the wet bulb temperature. For fit men, fully acclimatized to both dry and moist heat, 92 F. was the upper limit of wet bulb temperature at which they could march, in the nude, with a 20-pound pack at 3 miles per hour for 4 consecutive hours (work expenditure, 250 kilocalories per hour) without disability. When clothed in a single layer of Army fatigues of herringbone twill, the limiting wet bulb temperature was reduced to 90 F.40

The cooling power of the environment, also termed the "thermal acceptance of the environment" and defined as the amount of heat which a given environment can remove from the body surface of a workingman,41 was also studied. If a man, by his work activity, produced more heat than the environment could remove from his body surface, obviously his body temperature would rise and he became a candidate for heat casualty. On analysis, most of the deaths due to heatstroke (hyperpyrexia) in the Army stationed in the United States were found to have occurred where the "cooling power" of the environment was low, less than 500 Cal. per m.2 per hr. (calories per square meter of body surface per hour); a small number occurred where it was between 500 and 600 Cal. per m.2 per hr.; and very

37See footnote 35, p. 217.
38See footnote 19 (10), p. 213.
39(1) See footnote 3, p. 196; and footnote 17 (8), p. 212. (2) Eichna, L. W., Ashe, W. F., Jr., Bean, W. B., and Sheeley, W. B.: The Upper Limits of Environmental Heat and Humidity Tolerated by Acclimatized Men Working in Hot Environments. J. Indust. Hyg. & Toxicol. 27: 59-84, March 1945. (3) Robinson, S., Turrell, E, S., and Gerking, S. D.: Physiologically Equivalent Conditions of Air Temperature and Humidity. Am. J. Physiol. 143: 21-32, January 1945.
40Shelley, W. B., Eichna, L. W., and Horvath, S. M.: The Effect of Clothing on the Ability of Men to Work in Intense Heat. J. Clin. Invest. 25: 437-446, May 1946.
41(1) Report, Climatology and Environmental Protection, Research and Development Branch, Military Planning Division, Office of the Quartermaster General, 25 Aug. 1944, subject: Conference on the Principles of Environmental Stress on Soldiers for the Purpose of Developing a Climatic Index Suitable for Mapping Purposes for the Protection of Troops Operating in All Climates. (2) Report, Climatology and Environmental Protection, Research and Development Branch, Military Planning Division, Office of the Quartermaster General, 20 Aug. 1945, subject: Thermal Balance of the Human Body and Its Application as an Index of Climatic Stress. (3) Report, Climatology and Environmental Protection, Research and Development Branch, Military Planning Division, Office of the Quartermaster General, 17 Sept. 1945, subject: Thermal Acceptance Ratio.


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few, usually older obese soldiers, where the thermal acceptance of the environment exceeded 600 Cal. per m.2 per hour.42

Physical Fitness

A physically unfit man who is incapable of working in temperate climates at high levels of energy expenditure for as long as a fit man is at a much greater disadvantage in a hot environment. Lack of physical fitness contributed significantly to heat casualty in troops, chiefly in the United States. Mobilization suddenly subjected men to physical conditions requiring effort far beyond that to which they were accustomed. In temperate climates, most recruits were able to tolerate such increased physical activity, although inability to carry on was not infrequent. In hot climates, heat plus the exertion required produced a total load exceeding the physiological capabilities of many men, and casualty resulted. Thus, fatal heat casualties were more frequent in the United States than in any other theater. Furthermore, casualties were more frequent in men who were overweight, who were in the older age groups, and whose service in the Army had been of short (weeks to months) duration. Better physical fitness was believed to be an important factor in the lower incidence of heat casualty in units in hot theaters overseas than while in training in the United States.43

Heat casualty rates fell when the physical conditioning programs for recruits were guided by their performance and tolerance and when such programs were, at least initially, less accelerated in hot than in temperate environments. Good physical fitness does not, however, eliminate the need for acclimatization. Controlled observations have amply demonstrated that fit men also suffer disability on attempting hard work on first exposure to hot environments, although they acclimatize more rapidly than unfit men and, when acclimatized, are capable of working more efficiently.44

Sleep and Rest

Lack of sleep and rest in areas where high temperatures were sustained day and night predisposed to heat casualty. Men who worked on night shifts and then attempted to sleep during the day in quarters where air temperatures reached 120 to 135 F. (Iran) could not get adequate rest, and more rapidly became heat casualties. A cool place to sleep is the best preventive of heat disease among personnel. Men can tolerate through the day heat loads as great as any occurring naturally if they obtain adequate sleep and

42See footnote 16, p. 211.
43Pacific Warfare Board Report No. 60, U.S. Army Forces, Pacific, GHQ. 4 Sept. 1945, subject: Requirements of Tank Design and Operation in Relation to Effectiveness of Armored Personnel.
44(1) Adolph E. F.: Physiological Fitness for the Desert. Fed. Proc. 2: 158-164, 1943. (2) Johnson, R. E., and Robinson, S.: Selection of Men for Physical Work in Hot Weather. Report No. 16, Harvard Fatigue Laboratory, Contract No. OEM-cmr 54, for the Committee on Medical Research, Office of Scientific Research and Development.


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if they have comfortable quarters in which to relax and rest when not working.

Good housing in which men could sleep and relax, including air-conditioned barracks for night crews, was instrumental in lowering heat casualty rates in the Persian Gulf Command (p. 209). In desert areas, effective air conditioning was obtained by evaporative cooling, using simple "desert coolers,"45 boxes with 6-inch layers of excelsior over which water dripped slowly and, when obtainable, a fan blowing air over the box. Such devices would be of no value in the humid Tropics. But whether in the desert or the Tropics, fans were recommended, since the additional air movement produced a cooling effect.

Nutrition

In some hot areas, malnutrition apparently predisposed to heat casualty, particularly early in the war when much of the food was either packaged (C- and K-rations) or so dehydrated that it was unpalatable. Strict water rations made this food even less edible. Failure to eat led to loss of weight and occasionally to mild avitaminosis. Recommendations were made for better food, for less packaged food (the necessary packaged food in a more palatable and acceptable form), and for additional vitamins. As the rations improved, heat casualties decreased. Since, over the same period, more important corrective measures were also instituted, the role of improved nutrition in the reduced heat casualty rate cannot be evaluated. Medical officers in the field felt that an inadequate diet rendered the men more susceptible to heat casualty only when it produced definite malnutrition.

Controlled studies revealed that no known food factor will prevent the ill effects of heat and that the dietary requirements of men in the heat are essentially similar to those in temperate climates. There is the same need for the maintenance of caloric balance.46 The specific dynamic action of protein does not adversely affect the thermal equilibrium of men working in the heat.47 Vitamin losses in the sweat are negligible,48 even for the water-soluble vitamins (thiamine and ascorbic acid), and the vitamin requirements for work in the heat are not increased. At one time, vitamin C was thought to increase work efficiency in the heat and to prevent heat exhaustion, but this was subsequently disproved.49 Additional carbohydrates, such as glucose, are not helpful. A nutrition survey, including biochemical

45See footnotes 8 and 9, p. 206; and footnote 19 (5), p. 213.
46Johnson, R. E.: Nutritional Standards for Men in Tropical Climates. Gastroenterology 1: 832-840, September 1943.
47Pitts, G. C., Consolazio, F. C., and Johnson, R. E.: Dietary Protein and Physical Fitness in Temperate and Hot Environments. J. Nutrition 27: 497-508, June 1944.
48(1) Sargent, F., Robinson, P., and Johnson, R. E.: Water Soluble Vitamins in Sweat. J. Biol. Chem. 153: 285-294, April 1944. (2) Taylor, H. L.: Climate and Vitamin Requirements. Lancet 63: 358-359, November 1943.
49Henschel, A., Taylor, H. L., Brozek, J., Mickelsen, O., and Keys, A.: Vitamin C and Ability to Work in Hot Environments, Am. J. Trop. Med. 24: 259-265, July 1944.


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analyses of blood and urine of combat and garrison troops on several of the Pacific islands, revealed no deficiency of vitamins, protein, or hematopoietic factors in the men. Only occasional low values were found.

Overindulgence in alcohol led to heat casualty, but it is not possible to determine if alcohol alone or the dissipation associated with its use was the causative factor.

Clothing

Heat casualty directly attributable to clothing was difficult to establish. Men wearing heavy clothing, relatively impervious to air, tightly fitted over the body, with the closure of such ventilation ports as the trouser bottoms (by leggings), the sleeve openings (by wrist buttons), and the neck (by flaps and buttons), sustained an additional heat load. Many recommendations were made for light clothing, permeable to air, loosely fitting, and wherever feasible with neck, trouser bottoms, and sleeves open to permit greater ventilation of the body. These clothing specifications usually could not be met in the jungle climates, because of the necessity of covering as much of the body surface as possible and of closing all ventilation ports in order to avoid the insect vectors of many of the tropical diseases (malaria, dengue, filariasis, and scrub typhus). By the war's end, the use of insecticides and insect repellents suggested an avenue of investigation which might eventually permit the wearing of loose clothing in the Tropics with reasonable safety.

Clothing is undesirable in hot climates because it interferes with air movement over the body and thus hinders evaporative and convective cooling, the extent of this interference depending upon the type of cloth and its fit. Several quantitative studies have determined the heat loads of different clothing in various environments.50 Where the solar radiant heat is great and the evaporative gradient large, as in the desert, clothing is beneficial since it reduces the radiant heat load more than it interferes with the evaporation of sweat.51 Where both the radiant heat and the evaporative gradient are small, as in the Tropics, the net effect of clothing is harmful since it seriously hampers an important avenue of heat loss, evaporation of sweat and produces little benefit by reducing the already small radiant heat load.

Surgical operations in hot environments present serious difficulties. Extensive covering with sterile drapes greatly reduces heat elimination by patients. The administration of the usual preoperative atropine, by cur-

50(1) Report, Armored Medical Research Laboratory, Fort Knox, Ky., 17 July 1945, Project No. T-5, Test of Flameproofed Clothing, Physiological Effects of Wearing Flameproofed Clothing in Hot Environments. (2) Report, Armored Medical Research Laboratory, Fort Knox, Ky., 24 Nov. 1943, Project No. 2 (2-3, 18). Test of Adequacy and Ranges of Use of Clothing for Jungle Operations. Effects of Impregnated and Impervious Clothing Upon Efficiency of Personnel. (3) Robinson, S.: Committee on Medical Research Interim Report No. 12 (Revised), Indiana University Medical School, 2 Nov. 1944.
51See footnote 21 (3), p. 213.


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tailing sweating, greatly aggravated this difficulty. Certainly, anhidrotic drugs are to be avoided in any hot environment since they reduce evaporative cooling as an avenue of heat loss.

Previous and Associated Illnesses

Susceptibility to heat casualty was increased by intercurrent illness, no matter how mild; that is, venereal disease, upper respiratory infections, dysentery, overfatigue, constipation, immunizing inoculations, simple gastrointestinal disturbances, and diarrhea. The predisposing common denominator in these disturbances may have been the associated increased water losses. Return to duty too soon after recovery from any previous illness similarly predisposed to heat casualty, and convalescences had to be prolonged. Previous heat illnesses at times left men particularly prone to subsequent attacks. Medical officers soon realized that greater care, often to relieving men from duty, was required for disturbances which in temperate climates would have been unimportant.

Education

Indoctrination of each individual soldier for life in hot environments is essential to the avoidance of heat casualty. The war threw into the hottest of climates large numbers of men who had neither knowledge nor experience of how to live in the heat and who had to learn all of the acclimatization principles just discussed. These principles were disseminated through Circular Letters No. 11952 and No. 13653 from the Office of The Surgeon General. These letters did much to remove preconceived and erroneous ideas, particularly concerning water and salt requirements and workloads in the heat, factors which had led to most of the heat casualties. Beneficial results were quickly apparent. For example, a unit previously instructed and prepared, and adhering to these principles, moved from a camp in northern United States into the California desert and trained there without significant heat casualty.54

TREATMENT

The war experience contributed no new principles or methods to the treatment of heat casualty but provided a more complete evaluation of previously utilized, or suggested, therapeutic measures. This is important both because of the large number of men treated and because of the un-

52See footnote 26, p. 214.
53Circular Letter No. 136, Office of The Surgeon General, Army Service Forces, 28 July 1943, subject: Treatment of Heat Stroke, Heat Exhaustion and Heat Cramps.
54Annual Report, 51st Evacuation Hospital, for 1943.


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complicated nature of the heat casualties. They occurred in healthy young men, free from the associated, complicating diseases and disabilities so prevalent in civilian heat victims and so likely to confuse the analysis of therapeutic measures.

It is not the purpose of this report to review the various clinical types of heat casualty, but a brief description of the more important, or frequent, types of casualty encountered will be given. Heat cramp, due to loss of body salt, usually through sweating, is characterized by painful contractures of the voluntary muscles, especially of the abdominal wall; the rectal temperature is normal. Ill-defined effects of heat include such manifestations as a sense of overheating, fatigue, headache, giddiness, and skin rashes in an afebrile subject who, though ill and exhausted, can still move under his own power. Heat exhaustion is largely a circulatory fault characterized by a lowered blood volume, resulting from water loss (sweating) without adequate water replenishment. The temperature is normal or moderately elevated (102 F.). There is severe exhaustion, a cool wet skin, anorexia (at times with vomiting), giddiness, syncope (especially when erect), headache, evidence of dehydration, oliguria, and usually tachycardia. Hyperpyrexia (heatstroke) is characterized by a high rectal temperature, over 106 F.; by unconsciousness or delirium, often with convulsions; by circulatory collapse with shock; and by a hot dry skin without sweating. It probably results from a failure of the mechanisms for heat loss. Although each of these categories may be considered a separate clinical entity, not infrequently cases were encountered which did not fit into the accepted classification but showed manifestations of several categories; for example, "borderline hyperpyrexia" which showed symptoms of both heat exhaustion and heatstroke. Furthermore, some patients progressed from one category to another.

Mild cases.-The category of mild cases contains patients with ill-defined symptoms and those with heat exhaustion. The former required little more than rest, in as cool a place as possible, water and possibly salt, by mouth, and observation. Improvement was uniformly rapid, permitting return to quarters within several hours or the next day.

Heat exhaustion was treated much the same way, but the patients were usually hospitalized and treated longer and more intensively. When vomiting interfered with the oral intake, intravenous infusions of isotonic salt solution or of glucose in salt solution (2 to 3 liters) were given until fluids by mouth were retained. Only occasionally were stimulants necessary. Improvement was usually rapid and recovery complete in a day or two. Adequate convalescence was essential before return to full duty.

Both types of mild cases were at times considerably worse when enthusiastic but uninformed aidmen administered salt (usually tablets) with little or no water.55 Water is decidedly more important than salt for these

55See footnotes 29 (2) and (3) and 30 (2), p. 216.


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casualties, and salt alone is interdicted. Salt and water together constitute the optimal treatment.

The most important lesson learned from the mild heat casualties was the realization that all heat casualties are potentially serious and that the mildest of cases may deteriorate quickly and become dangerously ill. Before this was appreciated, men who appeared only slightly ill were frequently sent to their quarters (in some areas tents in which temperatures reached 120 to 137 F.) only to be found several hours later seriously ill and even comatose.56 Others would suddenly, and unaccountably, become critically ill, even while awaiting attention in busy aid stations or hospital waiting rooms.57 Again, men who appeared only mildly ill would collapse while being transported in trucks to hospitals at a distance and upon arrival would be in a serious condition.58 Heat casualty necessitated prompt "on the spot" and continued attention, and men sent to quarters required repeated checking just as well as those in hospitals.

Severe cases.-The category of severe cases contains patients with hyperpyrexia (heatstroke) and those with the more serious of the so-called borderline hyperpyrexias. Only the treatment of hyperpyrexia is discussed here; the treatment of borderline hyperpyrexia became an individualized intermediate regimen based upon the treatment schedules of mild and severe cases.

Treatment facilities.-Hyperpyrexia proved to be a true medical emergency.59 The high body temperature (107 to 112 F.), the cerebral disturbances of delirium, unconsciousness, and convulsions, and the circulatory shock required prompt, accurate diagnosis and quick, energetic treatment. Proper treatment could be instituted only by organizing in advance the required facilities and the trained personnel. Medical units in hot climates established heat casualty treatment centers consisting of treatment rooms, air conditioned when possible, which were provided with a plentiful supply of the coldest water available and equipped with sprays, fans, and special webbed treatment tables to provide access of air to the greatest possible skin surface. Some centers provided tubs for ice water baths. Well-ventilated, and where possible air-conditioned, wards were set aside for convalescence. In the desert, the air conditioning was easily obtained by desert coolers, already described; in the Tropics, air conditioning was virtually unobtainable. The treatment centers were staffed by trained teams prepared for immediate action. Such preparations played a very important part in the reduction of mortality due to heat casualty.

Reduction of body temperature.-Rapid lowering of the body temperature was the first, and the most important, factor in the treatment of

56See footnote 19 (5), p. 213.
57See footnote 19 (4), p. 213.
58Nayer, H. R.: Letter to the Editor, Journal, American Medical Association. J.A.M.A. 129: 1123, 15 Dec. 1945.
59(1) Annual Report, Station Hospital, Fort Eustis, Va., for 1943. (2) See footnote 35, p. 217.


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hyperpyrexia.60 The goal most frequently set was to lower the rectal temperature to 102 F. within 1 hour. Two approaches were utilized: (1) Evaporative cooling-wetting the patient completely and repeatedly with sprays of water and promoting evaporation of the water by fanning, and (2) conductive cooling-immersing the patient in a tub of cold water, containing ice when possible, and vigorously massaging the body while it was thus immersed.

There has been a long argument between the advocates of these two schools of treatment. Contention has centered about two points: (1) Whether ice or very cold water causes peripheral vasoconstriction which prevents blood from reaching the skin and thus hinders cooling and (2) whether evaporation of water is a more effective method of removing heat than the melting of ice and the subsequent heating of the cold water. From a physiological standpoint, the reasoning on these two points is as follows: Iced water can lower the skin temperature almost to zero, evaporation cannot lower it below the wet bulb temperature of the environment (70 to 80 F.). If there is no interference with the circulation of the blood through the skin, it follows that per unit time ice water will remove more heat from the blood perfusing the skin than will the evaporation of water from the skin. If, however, the cold water causes peripheral vasoconstriction, body cooling will be hindered. Accumulating evidence of successful and rapid lowering of high body temperature by the use of ice water suggests that, at the high body temperatures of heatstroke, undesirable peripheral vasoconstriction may not occur, particularly if the body is massaged. Therefore, rapid reduction in body temperature can be achieved.61 In regard to the amounts of heat removed by the evaporation of water and by the melting of ice, it is true that evaporation of water removes more heat than the melting of ice per unit mass of each. However, such an argument has force only for equal amounts (masses) of the two agents and does not apply where ample supplies of each are available to keep the body exposed to the lowest temperature each agent can produce. Furthermore, in humid hot environments, evaporation is bound to be slow and, therefore, cooling inefficient.

On the basis of the evidence and reasoning just presented,62 plus the accumulating experience from the field, the Army adopted, as the therapeutic procedure of choice for hyperpyrexia, the total immersion of the subject in cold, preferably iced, water with continuous massage of the body during the immersion.63 When ice is not available, the water must be changed

60(1) See footnote 9, p. 206; footnote 19 (4) and (5), p. 213; and footnote 35, p. 217. (2) Annual Report, 19th Field Hospital, for 1944. (3) Letter, Maj. John T. Larkin, MC, to The Surgeon General, 20 July 1945, subject: TB Med 175.
61Ferris, E. B., Jr., Blankenhorn, M. A., Robinson, H. W., and Cullen, G. E.: Heat Stroke; Clinical and Chemical Observations on 44 Cases. J. Clin. Invest. 17: 249-262, May 1938.
62Conference on Adverse Effects of Heat, Clinical Investigation Report No. 61, National Research Council, 3 Apr. 1945.
63War Department Technical Bulletin (TB MED) 175, June 1945, subject: Prevention and Treatment of Adverse Effects of Heat.


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often, or running water used. When water supplies are short, such expenditure may not be possible, and then evaporative cooling must be utilized. Since the effectiveness of evaporation depends on the velocity of airflow over the body, fanning becomes essential. Evaporative cooling was found most effective when the patient was nude, but one medical officer reported that cooling was most rapid from the completely wetted, clothed patient, presumably because of the increased surface area for cooling provided by the clothing.

Care was taken not to lower the rectal temperature too far, usually not below 102 F., although in one report no ill effects attended the lowering of temperature to between 99 and 100 F. Repeated checking of the rectal temperature at 10- to 15-minute intervals was considered necessary to control the period of rapid cooling. Thereafter, temperatures were taken at 30-minute intervals until they had stabilized below 102 F., for 6 to 8 hours. Repeated readings were necessary to detect the not infrequent return of body temperatures to high levels. When hyperthermia recurred, the cooling treatment was repeated.

Central nervous system effects.-Next in importance to lowering the body temperature was the treatment of the associated central nervous system effects. Of these, convulsions, often repeated, required prompt attention. Besides their usual undesirable effects, convulsions produce additional heat. Pentothal sodium (thiopental sodium) administered intravenously proved an effective therapeutic agent. Delirium and restlessness required treatment, usually with other, milder, sedatives, such as barbiturates and paraldehyde. For deep coma, stimulants were used, but usually in association with treatment of circulatory shock.

Parenteral fluids.-The cessation of sweating which occurs in hyperpyrexia usually prevents excessive fluid loss and dehydration, unless the latter is present before the onset of the heatstroke; for example, heat exhaustion progressing into hyperpyrexia. Although most patients with hyperpyrexia are not dehydrated, certainly not markedly so, the administration of fluid by all available routes was recommended. Intravenous infusions of isotonic salt solution, glucose, and particularly glucose in isotonic salt solutions were commonly used. The amount of fluid administered was governed by its need, overadministration being avoided. As treatment produced favorable results, fluids by mouth replaced the parenteral route.

Circulatory shock.-In the most severe hyperpyrexias, peripheral circulatory collapse with shock was commonly present. These patients were particularly prone to develop pulmonary edema (perhaps aided by too vigorous parenteral fluid therapy), of which death was the likely outcome. The treatment of the shock was the same as for any other circulatory shock of medical origin-and usually as unsuccessful. Plasma was given intravenously, 500 ml. at first and repeated after 30 to 45 minutes if there was no improvement. Various circulatory stimulants, such as Coramine


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(nikethamide), caffeine, sodium benzoate, ephedrine, and Metrazol (leptazol), were tried, usually without benefit. When pulmonary edema developed, inhalations of 100 percent oxygen and even venesection were employed, but atropine was specifically interdicted. The presence, or the development, of shock was of poor prognostic import.

Antibiotic medication.-In some instances, penicillin and the sulfonamides were administered on the possibility that some infection sensitive to these drugs was present in a masked form and contributing to the hyperpyrexia. This must always be considered in patients with hyperpyrexia for even a mild disease may be an important contributing factor. In other instances, heat casualties turned out to be severe cases of some other disease and required appropriate specific therapy. Proper diagnosis was especially important in those areas where severe and relatively unfamiliar diseases produced clinical pictures similar to heatstroke; for example, malaria. In some areas, an immediate malarial smear became a routine diagnostic procedure for all heatstrokes with the result that "on quite a few occasions the positive malarial smear cleared the picture * * *."64

Convalescence.-Following recovery from hyperpyrexia, long convalescences were the rule, at first in air-conditioned surroundings if possible. A too rapid return to duty frequently led only to a repetition of heat casualty. Since a number of these patients become sensitive to heat, the ability of convalescents to work in the heat should be tested under medical supervision before they are returned to full duty.

DETERIORATION DUE TO HEAT

The acute, casualty-producing effects of heat thus far discussed constituted but one phase of the heat casualty problem in hot climates. After men had learned to live in the heat so as to avoid acute casualty, there still remained the problem of the deleterious effects of prolonged stay in hot climates, generally believed to be a physical, physiological, and mental deterioration. Such deterioration is particularly likely where high temperatures are maintained during both the night and the day and throughout the year (Tropics) and less likely where there are seasonal variations in temperature with, in season, exceedingly hot days but usually cool nights (most deserts).

Deterioration did not occur in troops stationed in the hot areas of the United States since they never remained there long enough. In desert areas overseas, troops in the Persian Gulf Command definitely "slowed down" in the hot months, with a drop in morale and efficiency, but were not considered deteriorated since they still performed well under stress. The lassitude during the hot summer cleared quickly with the onset of cooler weather. Although some officers felt that both mental and physical deterioration due

64See footnote 19 (6), p. 213.


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to heat had appeared in some troops, the general opinion was that no real deterioration had occurred, even in troops who had been in this hot desert for 2 or 3 years.65

For the Tropics, the available data do not afford a definite answer. One survey specifically designed to study tropical deterioration indicated that, even after almost 4 years in the Southwest Pacific Area, troops remained physically fit and capable of performing hard work effectively.66 Nevertheless, there was a widespread feeling that the enervating effects of the hot climate "slowed the men down" and that "some reduction in efficiency in the absence of any disease seems unavoidable over a long period of time." The terms "loss of efficiency" and "deterioration" were used to cover a variety of manifestations noted in troops long in the Tropics; for example, lessened interest, lessened physical ability to perform at levels of ordinary capacity, increased irritability, lethargy, and lowered reserve stamina. Although these manifestations are not usually considered casualty producing, nevertheless they lowered the full efficiency of the commands and, in that sense, produce the same result as overt casualties. These "deteriorative" changes were usually noted after 8 to 12 months in the Tropics, while the first 2 to 4 months, after attaining acclimatization, were considered the period of maximum efficiency.

It is difficult to evaluate properly the "slowing down" and "loss of vigor" of troops long in the Tropics. The changes were not overt or marked and, on demand, work was still performed effectively. It was not possible to determine whether these changes were the result of true physical and physiological deterioration induced by the hot climate or the result of mental deterioration and lack of motivation of men too long in any undesirable surroundings regardless of climate. Controlled observations on troops in the Southwest Pacific Area suggested that there was no tropical deterioration as a specific entity differing from the deterioration in troops stationed elsewhere under similar circumstances, except for climate. Certainly, the monotony of the hot, humid climate and of the work, the lack of recreation, and the absence of long-accustomed amenities of life removed much, if not all, of the stimulus to exertion. The prevalence of skin disorders and tropical diseases constituted an added physical and mental drain. Thus, it is not possible to state whether true climatic deterioration, physiological or mental, or both, was present in these troops. Some loss of efficiency, whatever its origin, was present, but mild in degree and not limiting. Performance on demand, as in combat, was always high; when the demand relaxed, as in garrison duty, performance deteriorated. More careful observation and quantitative studies on troops in the Tropics are necessary to clarify the problem of climatic deterioration. Until this is accomplished, service of troops in the Tropics might well be limited to periods of 1 to 2 years, as suggested by commanding officers in these areas.

65See footnote 60 (2), p. 225.
66See footnote 34, p. 217.


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HYPOHIDROSIS SYNDROME

Out of the war experience came the description of the hypohidrosis syndrome, a new clinical syndrome to be added to the ill effects of heat. Described in 8 soldiers in the American desert,67 in 18 soldiers in Assam,68 and in a similar though milder form in British troops in southern Iraq,69 the manifestations of thermogenic anhidrosis or the hypohidrosis syndrome do not permit its inclusion in the standard classification of heat casualty. Isolated cases were also encountered in troops in Louisiana70 and in sailors in the Southwest Pacific.71

The essential features of this syndrome are (1) absence of sweating over most of the skin surface; (2) retention of sweating in profuse amounts in various limited areas (usually the face and then, in descending order, the axilla, the presternal area, and the interscapular area); (3) relatively mild and indefinite symptoms of overheating, weakness, dizziness, and headache; (4) diuresis; and (5) nondescript cutaneous changes from prickly heat and transient papules in some cases to a dry skin with fine branny desquamation in most instances. These changes were either sudden or gradual in onset. The syndrome occurred in men who had been in a hot area for some time and usually toward the close of a hot season. Most of the men had always sweated profusely and some noted episodes of particularly profuse sweating shortly before its cessation. All were aware that sweating had stopped and that the urine output had increased. Mild, indefinite subjective discomfort for several days preceded the seeking of medical care. Usually, the patients were not very ill and none had hyperpyrexia. Laboratory determinations have been few, but no abnormalities in blood chloride, calcium, phosphorus, blood count, or glucose tolerance were found in limited studies. The few skin biopsies examined did not show significant pathological changes in the sweat glands.72 On conservative treatment of rest in a cool place, recovery from subjective symptoms was usually rapid, and sweating returned spontaneously over periods varying from several weeks to several

67Wolkin, J., Goodman, J. I., and Kelley, W. E.: Failure of the Sweat Mechanism in the Desert; Thermogenic Anhidrosis. J.A.M.A. 124: 478-482, 19 Feb. 1944.
68Essential Technical Medical Data, U.S. Army Forces, China-Burma-India, for April 1945, dated 10 May 1945, with enclosure No. 1, subject: Hypohidrosis Syndrome-Report of Cases Seen at the 20th General Hospital, 18 Mar. 1945.
69LadeIl, W. S. S., Waterlow, J. C., and Hudson, M. F.: Desert Climate. Physiological and Clinical Observations. Lancet 2: 491, 14 Oct. 1944, and 527, 21 Oct. 1944.
70Blank, H.: Letter to the Editor, Journal, American Medical Association. J.A.M.A. 124: 1153, 15 Apr. 1944.
71Novy, F. G., Jr., and Ramsey, J. H.: Letter to the Editor, Journal, American Medical Association. J.A.M.A. 125: 738, 8 July 1944.
72(1) See footnote 68, above. (2) Postwar observations have established that the hypohidrosis syndrome results from the closure of sweat pores, usually by keratin plugs in the ostia of the sweat ducts. The surrounding areas are hyperkeratotic, but the walls of the sweat ducts remain intact. Sweat continues to be formed by the gland but is reabsorbed from the occluded duct and overt sweating does not occur. This sequence of changes accounts for the frequent cutaneous manifestations associated with the syndrome, the patchy nature of the anhidrotic areas, and the return of sweating with conservative therapy.


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months.73 In a few instances, large anhidrotic areas persisted for as long as 4 months. Followup studies, particularly on reexposure to external thermal stress, are not available.

The reason for the cessation of sweating is as yet unknown. The present belief inclines toward a functional rather than a pathological etiology, to a "fatigue" or "exhaustion" of the sweat mechanism without defining whether such fatigue is central (neurogenic) or peripheral (sweat gland) in origin.

In connection with this syndrome, it is of interest that approximately 15 percent of the racehorses imported from England and Ireland and raced in Trinidad, British West Indies, develop anhidrosois.74 Their performance suffers and the horses are removed from racing. In contrast to the laboratory findings in the hypohidrosis syndrome in man, these horses have a lowered blood chloride. When they are retired and turned out to pasture, there is a spontaneous recovery of their sweating mechanism associated with a return of the blood chloride to normal values. Anhidrosis has not been encountered in native horses or crossbreeds.

CONCLUSION

The experience of the Armed Forces in hot climates during World War II (and the almost identical experience of British troops)75 contains the solution of the problem of living and working efficiently and effectively in hot climates. The answer was learned at the expense of a goodly number of casualties and a fair number of deaths. The underlying principles should not be forgotten but should form a basis for the proper handling of troops in hot climates in future years. That man possesses physiological mechanisms which permit him to adapt to heat and that adherence to sound physiological principles will permit him to work hard, efficiently, and effectively in any naturally occurring hot environment can be concluded from this war experience. In closed spaces and in vehicles where the environment approaches or exceeds the physiologically tolerable upper limits of heat, cooling methods must be provided. The essential features of this review have been incorporated in War Department Technical Bulletin (TB MED) 175, June 1945,76 which is available for the lines of command as a basis of procedure in hot climates.

73Hyman, A B.: Some Histopathologic Aspects of Disturbances of Sweating. A.M.A. Arch. Dermat. 66: 145-151, August 1952.
74Special report, R. T. Gaylor, subject: Chronic Anhidrosis With Lowered Blood Chlorides in Race Horses at Trinidad, B.W.I.
75(1) MacLean, K. A.: Observations on Sunstroke and Heat Exhaustion in Tropics. J. Roy. Nav. M. Serv. 29: 31-36, January 1943. (2) Morton, T. C.: Heat Effects in British Service Personnel in Iraq. Tr. Roy. Soc. Trop. Med. & Hyg. 37: 347-372, May 1944. (3) Palmer, H. A.: Case Report of Psychosis Following Heat Stroke. J. Roy. Army M. Corps 82: 186-189, April 1944. (4) Croom, J. H.: Effects of Heat; Account of Group of Cases Admitted to a General Hospital on Arrival in the Middle East. J. Roy. Army M. Corps 83: 288-292, December 1944. (5) Sheperd, H. M. D.: Effects of Heat in Iraq. J. Roy. Army M. Corps 84: 1-8, January 1945. (6) Critchley, M.: Problems of Naval Warfare Under Climatic Extremes. Brit. M.J. 2: 145, 4 Aug. 1945; 173, 11 Aug. 1945; and 208, 18 Aug 1945. (Croonian Lectures.) (7) Stenning, J. C.: Salt Deficiency States in Tropical Climate. J. Roy. Nav. M. Serv. 31: 129-146, July 1945.
76Superseded by TB MED 175, 7 Aug. 1957.

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