"WHITB RACE IN THE TROPICS — WARD 565 



view, even be impossible, nevertheless there is a line of demarcation 

 between the two, however faint it may be, and however difficult it 

 may be to draw. 



The uniformly hiprh temperatures of (he Tropics — llie well-known 

 tropical monotony of heat — when combined with hiph humidity and 

 the characteristically small variability of temperature from day to 

 day, have certain already fairly well re^o^ized physioloj^ical effects, 

 although definite numerical measurements are still lo a lar«i:e extent 

 not yet available, and much of the evidence is conflictin<2:. On the 

 basis of recent studies, the body temperature seems, in general, to 

 be essentially the same as elsewhere when the body is at rest, but 

 with exercise it rises more rapidly than in cooler climates, and also 

 falls more slowly. Much exercise has the same effect as a mild fever. 

 The respiration rate is hiirh, probably because of the body's attempt 

 to increase evaporation and so to reduce its temperature. There is 

 evidence to indicate that evaporation from lungs and skin is far 

 more concerned in controlling the body temperature than is chem- 

 ical activity. The blood pressure apparently shows no permanent 

 change, but there seem to be greater temporary variations after 

 exercise than is the ca^e in temperate climates. As regards the 

 composition of the blood, there is a slight relative decrease in the 

 number of red corpuscles, but the specific gravity shows no change 

 except in disease. It appears that the popular belief in a " thinness 

 of the blood " after prolonged residence in the Tropics is unfounded, 

 except, as just stated, in the case of disease or of anemia. Perspira- 

 tion is profuse. There is, in general, an increased activity of the 

 liver, kidneys, and spleen, as contrasted with an increased activity 

 of the organs of respiration in higher latitudes. It would seem that 

 when the white man goes to live in the Tropics his first functional 

 disturbances are likely to be in the intestinal organs, and may 

 predispose to dysentery or other dangerous diseases. Per contra, 

 when human beings or animals are brought from the Tropics to 

 higher latitudes, where there are lower temperatures and greater 

 variability of weather, the troubles which they experience are mostly 

 pulmonary. It appears that, on the whole, the measurable physio- 

 logical disturbances are not very significant, in so far, at lea.st, as 

 our pre.sent data go. There are, however, nonmeasurable nervous 

 effects which may be much more critical and fundamental in the 

 problem of acclimatization. Dr. B. C. Crowell, in an address before 

 the American Philosophical Society, five years ago (1925), said, 

 in speaking of the effects of tropical climates upon white men, 

 "Science has not been able to measure the unque.sti(mably harmful 

 influence on the nervous .system of a constant temperature, bright 

 sunshine, bnlliant colors, and the absence of seasonal variations." 

 28095—31 37 



