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Scientific Proceedings (126) 



conditions of roomlight, would lead to the development of both 

 rickets and xerophthalmia and of xerophthalmia alone. If this 

 information could be ascertained it would be a valuable con- 

 tribution to the study of xerophthalmia and by analogy would 

 suggest either the unity or the divisibility of the factors con- 

 tained in cod liver oil, which prevent and cure both xerophthalmia 

 and rickets. It was desired also to determine whether or not 

 different combinations or groups of light rays — as for example, 

 direct sunlight, quartz lamp radiations and roomlight — have the 

 same or similar influence upon rats fed xerophthalmia produc- 

 ing diets. It was conceivable also that complete absence of light 

 rays might have a different effect upon experimental animals 

 than that produced by radiations showing either a complete 

 solar spectrum (direct sunlight) or spectra considerably differ- 

 ent from sunlight (quartz lamp radiation and roomlight). 



On October 22, 1921, fifteen young albino rats were placed 

 on a diet low in fat-soluble A and phosphorus (3127). Pre- 

 vious experience had shown that young rats on this diet would 

 develop rickets and xerophthalmia. The animals were divided 

 into three groups of five each. One group was to be kept in a 

 laboratory room screened with ordinary window glass ; a second 

 group was to be kept in total darkness, excepting for the rays 

 from a red electric light bulb such as is used in photographic 

 dark rooms 1 ; the third group was to be kept in ordinary room- 

 light, but was to be radiated with a mercury vapor quartz lamp. 

 On November 15, 1921 another experiment was started using 

 twenty-six young albino rats. These animals were placed on a 

 diet low in fat-soluble A and poor in proteins of good quality 

 (3392). Previous experiments had shown that this diet pro- 

 duces xerophthalmia in young rats. These animals were divided 

 into groups and subjected to the same experimental conditions 

 as detailed above. In these preliminary experiments it was found 

 that all of the animals failed to grow, became emaciated and 

 developed xerophthalmia. On the doubly deficient diet only the 

 rats treated with the violet rays failed to develop rickets. 



It was decided to repeat these preliminary experiments under 

 conditions more favorable for study, and in addition to ex- 

 pose rats to the effect of direct sunlight. Accordingly, on April 



1 This bulb was lighted only when the animals were being fed or in- 

 spected. 



