536 PHALEN. 



bra} T shirt, but the blue and olive-drab flannel shirts were shown to be not ' 

 nearly so protective chemically as would be expected. 



It is a widely, but not universally accepted theory that the pigment 

 in the skin of the dark-hued races is an effect of the chemical rays of the 

 sun, and that its purpose is to protect the organism from the deleterious 

 influence of these rays. Certain it is that sunlight increases the deposi- 

 tion of pigment in the skin as it shoAvn by tanning in the white race. 

 That the dark pigment of the Malay or the Negro is due to a like 

 cause is not so apparent and that it was deposited for the purpose of 

 protection from the sun is rather difficult of proof. If a determination 

 of the chemical nature of the skin pigments of the different colored races 

 has ever been made I am unaware of it. Sambon, of London, photo- 

 graphed the spectrum of an electric arc lamp after passing the rays 

 through the skin of a native of India and then constructed a cloth that 

 would have the same effect. This cloth was of a dark color externally, 

 and red inside. 



To determine the relative opacity of the skin of different degrees of 

 pigmentation, specimens were obtained from an exceptionally white sub- 

 ject, from a light Filipino, and from one of the darkest subjects obtainable. 

 These specimens were subjected to the same photographic tests as the 

 fabrics mentioned above. The skin specimens were first prepared by 

 removing all subcutaneous' tissue and making them as nearly as .possible 

 of uniform thickness. By reference to a series of photographs, compar- 

 ing the very dark skin with the white, it could be seen that the former, 

 as expected, was more resistant to light than the latter. The difference 

 was most noticeable for the shorter exposures, being much less so as the 

 time of exposure is increased. It could be seen that the white skin was 

 quite opaque to the chemical rays, and that when the time of exposure 

 was increased to one minute the effects on the photographic plates did 

 not differ very greatly. The effect upon the plate produced by a one- 

 minute exposure through the dark skin was approximated in about one- 

 fourth that time through the white. A comparison of the effect produced 

 through the light brown and the white skins gave almost no difference 

 in their degrees of opacity during a fifteen-second exposure, and those 

 of less duration piroduced no greater variation. The added effect of 

 the texture of the skin was shown. Both the white and the dark brown 

 were firm and tough, while the light brown was of a much softer texture. 

 It is apparent that the superior density of the white skin has compensated 

 for the increased pigment of the light Malay. Another photograph was 

 made giving a fifteen-second exposure through the darkest skin and 

 through the white skin reinforced by one layer of khaki uniform cloth. 

 It was observed that the khaki material completely neutralized the 

 difference in opacity which exists between the two. 



A comparison of these photographs with those made through the 

 fabrics showed another important fact. It will readily be seen that the 



