546 PHALEN. 



creased temperature, pulse, and respiration, with heat strokes and feb- 

 ricula, is felt by the system during the hot and moist days of May to 

 October rather than during the bright days of January to May. The 

 role that humidity plays as an adjunct to heat is that of an interference 

 with heat loss by evaporation. As evaporation from the skin is the main 

 process by which a balance is maintained between heat production and 

 heat loss, such an interference is serious. With a high external tem- 

 perature and heat loss practically abolished by humidity, we have, as 

 Sutton says, a vicious circle established. With the rise of internal tem- 

 perature, oxidation in the system is increased with production of more 

 heat and a still greater rise in body temperature. The progressive action 

 of these factors on temperature, pulse and respiration are well illustrated 

 in the experiments with moist heat described heretofore. 



The photographic work with skins of varying pigmentation suggests 

 that such pigment is of no great protection from actinic rays. It is prob- 

 able that the effects of the chemical ray are exhausted upon the skin alone. 

 Even in the deeper layers of the skin there is a constantly circulating 

 layer of blood which is probably much more efficient as a protection 

 against the chemical ray than is the permanent layer of pigment. If 

 the effect upon the skin can be accepted as a measure of actinic influence, 

 then the khaki is of itself sufficiently protective. Many men have their 

 arms protected only by one layer of khaki material and after years of 

 service in the Tropics have no more pigment in the skin thereof than they 

 had upon arrival. 



A final judgment then is that the test underclothing has added 

 materially to the burden of heat upon the system, a burden which un- 

 doubtedly is the great cause of tropical deterioration. To balance this, 

 it is protective against the chemical ray, the influence of which is regarded 

 as of little moment, and which is sufficiently excluded by khaki clothing 

 and the campaign hat worn at present. Certainly no beneficial effect 

 whatever was observed from the use of this clothing. This experiment 

 suggests that any efforts toward increasing the physical well-being and 

 efficiency of the soldier shall be directed toward protecting him from the 

 debilitating effects of heat and humidity. One effect quite aside from 

 these factors is that upon the eyes. We see here the result of the sun- 

 light in many distressing symptoms, but these are probably due to the 

 light rather than to the chemical rays. Any protection afforded the 

 eyes from the glare of the tropical sun deserves to be heartily wel- 

 comed. 



In closing I wish again to acknowledge the valuable work clone by 

 Major C. C. Collins, Lieutenants G. L. McKinney, Hiram A. Philipps, 

 and C. D. Cowles, Jr., Medical Corps, in supervising the details of this 

 test. Credit is also due to Captain Henry J. Nichols, Medical Corps, for 

 assistance in outlining the experiment, and to Captain James D. Fife, 

 Medical Corps, who placed his photographic appliances at our disposal. 



