564 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 30 



lives, has been carried on for some years by the Rockefeller Institute 

 for Medical Research. An outbreak of yellow fever in Brazil during 

 the summer of 1928 showed that South America is not yet safe 

 from this disease. Definite temperature controls over the occurrence 

 of yellow fever have long been known, and stated in specific num- 

 bers of degrees of the thermometer scale, and the disappearance of 

 epidemics when the freezing point is reached was noted several 

 decades ago. 



Sunstroke and heat prostration, as is to be expected, are most com- 

 mon in the Tropics. Exposure to the sun does not always explain 

 sunstroke, for at sea the tropical sun is much less fatal than on land, 

 and places with apparently similar conditions of sunshine differ much 

 as regards prevalence of sunstroke. The story is told of a planter 

 from Barbados who had gone to live in Madras, and who insisted on 

 riding horseback in the sun as he had been accustomed to do in 

 Barbados. He laughed at friends who warned him against running 

 this risk, and lost his life by sunstroke. At Panama there were only 

 two deaths from sunstroke and 21 cases of heat exhaustion in a popu- 

 lation of 120,000, in 13 years. In Liberia, on the other hand, it has 

 been pointed out by Dr. C. F. Brooks that in climatic conditions on 

 the coastal lowlands much like those of the Atlantic coast of Panama, 

 manual labor such as is performed by white men in Panama is im- 

 possible, and only a few minutes' exposure is enough to give " a touch 

 of the sun." It has been suggested that an explanation may perhaps 

 be found in the fact that in Panama protection against the sun is 

 provided by a moist layer of air which extends to great heights, 

 Avhile in Liberia the moist layer is relatively thin. Very damp air, 

 combined with strong sunshine, induces heat exhaustion at fairly 

 moderate temperatures, and most damp lowlands in the Tropics are 

 dangerous for white men who are doing manual labor, or who have 

 their heads unprotected. Apparently, either intense sunshine alone, 

 or very damp air alone, is not dangerous. It is the combination of 

 the two that brings fatal results. On the wharves of Calcutta there 

 used, to be painted, in large white letters, the significant warning, 

 " Beware of the sun," so that persons coming there for the first time 

 from the British Isles would read those words before they set foot on 

 shore. " Beware of the sun " is a good rule for the Tropics. There 

 is, in general, too much sunshine in the Tropics. The skin of white 

 persons exposed to the sun there often becomes badly burned and 

 blistered, and travelers commonly suffer because of lack of protec- 

 tion of neck and limbs under the hot tropical sun. 



The second aspect of the health and acclimatization of the white 

 race in the Tropics concerns the physiological disturbances. While 

 the separation of the effects of physiological disturbances from 

 specific diseases is difficult, and may, from a strictly medical point of 



