THE 



POPULAR SCIENCE 



MONTHLY. 



JUNE, 1912 

 TEOPICAL SUNLIGHT^ 



By Dr. PAUL C. FREER 



LATELY DIEECTOK OF THE BCKEAU OF SCIEXCE. ilAXILA 



THE subject of the influence of sunlight in the tropics has been the 

 subject of extended discussion for many years, and the general 

 opinion seems to be that the intensity of insolation is the most impor- 

 tant factor influencing the pliysical welfare of the white inhabitants 

 in those parts of the world lying within the regions which are generally 

 considered as having a tropical climate. In considering the question of 

 what may be regarded as a tropical climate, we are too apt to be influ- 

 enced by preconceived opinions as to what the dominating factors are, 

 and we are prone to lose sight of the fact that there is as much differ- 

 ence between trojjical climates as between those in the temperate zones. 

 Persons living in the tropics are almost certain, during their early 

 years of residence, through ignorance or otherwise, radically to change 

 their mode of living and subject themselves to hygienic conditions which 

 they would consider inadmissible in their former homes. The races of 

 people native to the tropical zones have no knowledge of bacteriology 

 and pathology which would enable them to understand the measures to 

 be taken to avoid infectious and other diseases, whereas they live in 

 regions where the absence of a pronounced winter is favorable to the 

 rich development of microscopical life. As a consequence, many of the 

 ill effects which are attributed to sunlight may in reality be due to 

 entirely different causes. Again, races native in the tropics, as a rule, 

 do not have access to the complete food supplies of persons in temperate 



^ The manuscript of this article was received by the editor two weeks after 

 the cabled announcement of the lamented death of Dr. Freer. Dr. Freer had 

 attained high distinction as a chemist and since taking charge of the scientific 

 work of the government in the Philippines in 1901, had contributed greatly to 

 the organization and advancement of the scientific work under our government. 



VOL. LXXX. — 3.'i. 



