428 CHAMBERLAIN. 



PART I. INTRODUCTION; SOURCES OF EVIDENCE; GEOGRAPHY AND CLIMATE; 



SUNLIGHT. 



INTEODUCTION. 



The influence of a tropical climate on men, especially the members of 

 the Caucasian race, is an extremely complex subject. Among the general 

 factors to which, with greater or less weight of authority, the deleterious 

 effects of tropical residence are alleged to be due may ^be mentioned 

 heat, humidity, chemical action of the sunlight, lack of exercise, dis- 

 turbed sleep, improper food, bad water, alcoholic and venereal excesses, 

 and, perhaps most important of all, infections with those animal and 

 vegetable pathogenic organisms which are confined more or less exclusively 

 to hot regions. Individiially age, sex, race, stature, previous residence, per- 

 sonal immunity, and perhaps complexion have to be given consideration. 



The work herein reported has to do with only one of the above factors, 

 namely the complexion type.- The distribution of the black and brown 

 races in the hotter portions of the globe and the difficulties which in 

 the past attended the colonization of the Tropics by the Caucasian were 

 matters of common observation long before the causes of tropical -disease 

 and deterioration received any adequate study. More recently several 

 authors have claimed that the blonds tend to decrease in numbers or to 

 deteriorate when they are transplanted from the relatively cloudy regions 

 of northern Europe to sections in the Temperate Zone which have a 

 much greater amount of sunshine. Woodruff, studying this phase of 

 the subject in the Philippines, maintains that the blonds suffer more 

 severely than do the brunettes from the deleterious influence of tropical 

 residence and that the ill effects observed among white men dwelling in 

 the Torrid Zone ai'e due mainly to the large proportion of chemical or 

 ultra-violet rays contained in the tropical sunlight. (2) (3) 



To determine what may be the influence of the actinic rays alone, as 

 distinguished from the other factors enumerated in the first paragraph, 

 is evidently well-nigh impossible. The question as to whether trans- 

 planted fair-skinned races gradually change after many generations from 

 a lighter to a darker average type, as a result of the survival of those 

 best fitted to endure a high degree of sunlight, is purely speculative and 

 of theoretical interest only. Whether men of dark complexion living 

 ten, twenty, or thirty years in the Tropics can withstand the climatic 

 influences more successfully than those having fair skin, light hair, 

 and blue eyes is of much practical importance, but is extremely difficult 

 to determine because of the almost insurmountable obstacles which stand 

 in the way of making observations over such a period of time on any 

 considerable group of men. When it comes to the relative resistance 

 of the blonds and the brunettes during the comparatively short tour of 

 duty (two years) which American soldiers commonly serve in the Phil- 



