NECROSIS 375 



fouiul that inodcmte action of electric light, rich in violet and ultra- 

 violet raj's, causes mitotic cell division; if the action is stronger, the 

 cells undergo amitotic division and then become necrotic. Blue rays 

 have but slight cytotoxic action, and rays further towards the red end 

 of the spectrum are without demonstrable cffec '.. Light baths are 

 said by Oerum"' to increase greatly the quantity of corpuscles and hemo- 

 globin, while residence in the dark reduces these elements. The de- 

 struction of bacteria by light is a well-known phenomenon, ^^ but it 

 has been suggested that their destruction depends rather upon the 

 action of substances produced in the culture-medium under the influ- 

 ence of light than upon the effect of the hght upon the bacterial cells 

 themselves. In view of the fact that enzymes and antibodies in solu- 

 tion are quite readily weakened or destroyed by the action of light, it 

 is possible that intracellular enzymes may be similarly destroyed by 

 light, with resulting cell death. However, in the case of bacteria, at 

 least, the effects of light seem to depend upon oxidation processes, for 

 in the absence of oxygen, bacteria are not seriously injured by light, 

 and D'Arc}^ and Hardy^* found that "active oxygen" is formed by 

 the same portion of the spectrum that is most active in destroying 

 bacteria. ^^ Light may also alter the solubility of cell proteins, espe- 

 cially in the presence of various organic and inorganic substances that 

 act as sensitizers, such as silica"! es, sugar, lactic acid or urea.^*^ In 

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



The general effect of light acting on organic substances present in 

 plant and animal cells, is to produce from carbonyl-containing materi- 

 als aldehyde or ketone compounds, whose reactivity and availability 

 for important synthetic changes are conspicuous (Neuberg).*^ 

 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. 



36 Pfluger's Arch., 1906 (114), 1. 



3' Literature given by Wiesner, Arch. f«Hyg., 1907 (61), 1. 



38 Jour, of Physiol., 1895 (17), 390. 



33 See also Agulhon, who found that ultraviolet rays may attack enzymes to 

 some extent in the absence of oxygen (Ann. Inst. Pasteur., 1912 (26), 38). 



"Schanz, Biochem. Zeit., 1915 (71), 406; Arch. Ophthal., 1918 (96), 172; 

 Burge, Amer. Jour. Physiol., 1916 (39), 335; Neuberg and Schwarz, Berl. klin. 

 Woch^ 1917 (54), 84. 



" Biochem. Jour., 1908 (13), 305. 



"See Davenport, "Experimental Morphology," 1897, p. 162. 



" Miinch. med. Woch., 1912 (59), 2795. 



