84 



Scientific Proceedings (126) 



(3127) was maintained and in those on the diet producing xero- 

 phthalmia alone (3392) never entirely lost. 



Exposure to direct sunlight protects rats from xerophthalmia 

 to a limited degree, dependent in part at least on the extent of 

 the dietary deficiency in fat-soluble A and in other factors, par- 

 ticularly proteins of good quality and upon the duration and 

 constancy of the exposure. In some animals the disease develops 

 regardless of sunlight; in others it is on the surface or just sub- 

 merged; while in a few it never develops at all. 



In this paper when the expression "exposure to direct sun- 

 light" is used, it is inclusive of all that is ordinarily indissoluhly 

 associated with sunlight exposures. Sunlight itself, the effect of 

 changes in the atmosphere by solar radiation, temperature, out- 

 of-door air, these and other factors unknown to us acting singly 

 or in combination may be responsible for the results usually at- 

 tributed simply to "sunlight." 2 These experiments bring out 

 above all else that exposure to direct sunlight and out-of-door 

 air promotes in a very wonderful way the health, bodily vigor 

 and longevity of animals which otherwise are unable to adapt 

 themselves to markedly adverse environmental conditions. 



Sunlight probably exerts no specific anti-xerophthalmic in- 

 fluence but acts by raising the level of the cellular activity of 

 the organism to a point where the progress of the disease is 

 held in check or allowed to advance very slowly and with rela- 

 tively little disturbance. 



Previous experiments have shown that sunlight contains an 

 equivalent of the unknown factor in cod liver oil which pro- 

 motes the normal formation of bone and in that sense may be 

 spoken of as anti-rachitic. The experiments herein reported 

 indicate that sunlight does not contain at all or only to a very 

 slight degree the equivalent of the anti-xerophthalmic factor 

 in cod liver oil — fat-soluble A. 



By analogy, therefore, these experiments suggest that there 

 are in cod liver oil two distinct factors — one preventive and 

 curative of rickets, and the other preventive and curative of 

 xerophthalmia. Sunlight can compensate for the absence of 

 the one but not completely of the other. 



2 Experiments are now in progress which seem to indicate that out-of-door 

 air does have a favorable influence upon rats fed a rickots-producing diet. 



