CAUSKH OF SECR08L-! 375 



Lacteria.-" Li<iht may aiso alter tlie soluliility of cell jiroteiiis, cspe- 

 oiallj' in the ]H"eseiK'e of various organic; and iiior^nuiic substances that 

 act as sensitizers, such as silicates, sug-ar, lactic acid or urea.-'"' In 

 this may lie the cause of cataract, especially diabetic cataract. 



The general effect of "light acting on oi-ganic substances present in 

 plant and animal cells, is to })roduce from earbonyl-containing materi- 

 als aldehyde or ketone compounds, whose reactivity and availability 

 for important synthetic changes are conspicuous (Xeuberg).^'' 

 Whether oxidative processes are the cause of death in animal cells is 

 not known, but we are familiar with many chemical reactions of vari- 

 ous sorts that are initiated or checked by the action of light. ^^ Thus, 

 bilirubin is oxidized into biliverdin, when acted upon by sunlight, 

 even when not in contact with air; many vegetable oils are oxidized 

 by sunlight, and it is probable that the oxidizing action of light upon 

 organic compounds is of wide-spread occurrence. It is, therefore, 

 quite possible that such oxidative changes may be the cause of necrosis 

 produced by the action of light rays, especially as Bering ^- has found 

 that chemically active light rays have a direct action on oxidizing 

 enzymes. 



It is very probable that not all of the effects of exposure to the sun 

 depend upon the heat rays, for there is evidence that the light rays 

 may also produce effects. This is definitely true in the case of indi- 

 viduals or animals with certain pigments in their blood, notably 

 liematoporphyrin (q. i\). In them, not only may skin eruptions re- 

 sult from relatively small exposure to light, but mice may be so sen- 

 sitized that a few moments of exposure to light is fatal. ^-'^ Artificial 

 fluorescent substances, such as eosin, also sensitize tissues and proteins 

 to light."-'' Normal blood absorbs light rays in large amounts, as 

 Finsen showed, and it is quite possible that changes in the ehemistrv 

 of the blood result from the light rays. Exposure to the sun may 

 cause a general leucocytosis with relative lymphocytosis.^-*^ 



According to Hertel ^^ the idtravlolet rays cause oxygen to split off 

 the easily oxidizable compounds of protoplasm, and Bovie ^* found 

 that they coagulate proteins ; they also have a destructive effect on 

 enzymes -'' and hormones.^^'' Toxins, like enzymes, are reduced in 

 activity by ultraviolet rays.^*" 



29 See also Agulhon, who found that ultraviolet ravs may attack enzymes to 

 some extent in the absence of oxygen (Ann. Inst. Pasteur.. 1912 (20), 8S). 



29aSchanz, Biochem. Zeit., 1915 (71), 406: Burge. Amer. .Jour. Phvsiol.. I'.tlti 

 (39), 3.35. 



30 Biochem. Jour., 190S (13). 305. 



31 See Davenport. "Experimental ^forpliologv," 1897, p. 102. 

 32Miinch. med. Woch.. 1912 (59). 2795. 



32aHausmann, Biochem. Zeit.. 1914 (67). 309. 



32b Pincussohn, Deut. med. Woch., 1913 (44), 2143. 



32c Aschenheim. Zeit. Kinderheilk., 1913 (9), 87. 



33 Zeit. AuGfenlieilk., 1911 (26), 393. 



34 Science, 1913 (37), 24: see also Burge. Amer. Jour. Plivsiol., 1910 (39). 335. 

 34ii Burge et a/., Ainer. Jour. Physiol., 1916 (40). 426. 



34bHartoch ef nl.. Zeit. Immunit'iit., 1914 (21), 643. 



