434 CHAMBERLAIN. 



those of the blond type. The subject needs much more study before a 

 definite conclusion can be reached regarding the influence of the chemical 

 rays of the solar spectrum, but the recent work by Aron(4) seems to 

 indicate that the deleterious influence of the tropical sunlight on men 

 and animals is due to the long heat-rays rather than to the short length 

 ultra-violet waves. Steinmetz(5) considers ultra-violet radiations of 

 moderate intensity, such as occur in sunlight, to be harmless to the 

 eyes. When acting on the skin ultra-violet rays have little power 

 of penetration, being absorbed by the blood, but whether they can 

 produce such changes in that fluid as to lead to constitutional disturb- 

 ances still remains an unsettled problem. 



PART II. PHYSICAL EXAMINATIONS AND LABOEATORY TESTS ON BLONDS 

 AND BRUNETTES OF THE 1909-GROUr AND TITK 1910-GROUI'. 



The work on the 1909-Group began in the first quarter of 1909 and 

 ended in December of that year, there being records for each man of 4 

 observations evenly spaced over an interval of about eleven months. 

 The examinations of the 1910-Group began in the second quarter of the 

 year 1910 and ended at the same time in 1911, there being for each 

 soldier 5 complete observations spaced at approximately three-month- 

 intervals during the period of one year. The observations were made 

 under our supervision by the gentlemen named in footnotes 3 and 5. 

 All of these officers are thoroughly familiar with the laboratory methods 

 involved in the work, and the numbei' of observers minimizes the in^ 

 fluence of the personal equation. 



It should be understood that the men under observation wei'e healthy soldiers, 

 any who showed evidence of disease having been excluded before the beginning 

 of the observation period. The length of time the men had served continuously 

 in the Philippines at the eommeneement of the test varied from two months to 

 several years." The average length of the present tour of tropical service at the 

 beginning of the year of observation was in the 1909-Group for the blonds 14.9 

 months and for the brunettes the same. In the 1910-Group it was for the 

 blonds 6.4 and for the brunettes 6.7 months. In both groups it will be seen that 

 the average period of tropical service prior to the commencement of the observa- 

 tions was sufficient for the preliminary stimulating effect of the Tropics to have 

 passed away. At the beginning of the observation period the total tropical 

 service, including present and previous tours, in the 1910-Group was 32.9 months 

 for the blonds and 34.4 months for the brunettes. In the 1909-Group the average 

 height was the same for both blonds and brunettes, 67.4 inches (171.1 centimeters), 

 and the average age was practically the same, 25.5 years for the blonds and 

 25.1 for the brunettes. In the 1910-Group the average height was 67.8 inches 

 (172.2 centimeters) for the blonds and 67.3 inches (170.9 centimeters) for the 

 brunettes, and the average age was 27.4 years for the blonds and 28.1 years for 

 the brunettes. 



"• The men with seveial years' service had voluntarily transferred from organ- 

 izations going home to others just arriving in the Islands. One man we have 

 in mind was a most conspicious blond and had been twelve years continuously 

 in the Philippines, remaining in perfect health. 



