CAUSES OF NECROSIS 313 



employed for transfusion without causing hemoglobinuria. 

 Grawitz saw motion persist in human ciliated epithelium kept 

 for seven to nine days on ice. Ciliated epithelium from the mouth 

 of the frog may survive cooling to 90, and frog eggs are not 

 killed by 60. In many cells, however, the physical changes 

 produced by freezing, and also by the subsequent thawing, are 

 sufficient to render them incapable of further existence. Cells 

 devoid of or poor in water cannot be killed by freezing, hence 

 it is probable that the currents set up about the crystals of ice 

 in thawing, as well as the rapid contraction and expansion under 

 the influence of the cold and the ice formation, are the cause of 

 the effects of freezing, which, therefore, are not dependent upon 

 chemical, but upon physical, alterations. 



In the case of warm-blooded animals, the gangrene following 

 freezing depends not so much upon the freezing of the cells 

 themselves as upon the formation of hyaline thrombi in the 

 injured vessels (v. Recklinghausen, Hodara 1 ). Kriege 2 found 

 that if the freezing is transitory, the thrombi may again 

 disappear ; if over two hours in duration, they are persistent. 

 Rischpler, 3 however, considers that cell death is due primarily 

 to the effect of the cold upon the cells. 



I/ight. Light may affect tissues seriously, apart from the 

 effects of accompanying heat. In the treatment of lupus by 

 the Finsen method with concentrated light rays, the action is 

 largely a stimulating one, but associated with or subsequent to 

 a certain degree of cell injury. Ogneff 4 found that moderate 

 action of electric light, rich in violet and ultraviolet rays, 

 causes mitotic cell division ; if the action is stronger, the cells 

 undergo amitotic division and then become necrotic. The 

 destruction 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 influence of light than upon the effect of the light 

 upon the bacterial cells themselves. In view of the fact that 

 enzymes in solution 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. How- 

 ever, in the case of bacteria, at least, the effects of light seem 

 to depend upon oxidation processes, for in the absence of oxy- 

 gen, bacteria are not seriously injured by light, and D'Arcy and 

 Hardy 5 found that " active oxygen " is formed by the same 



1 Munch, med. Woch., 1896 (43), 341. 2 Virchow's Arch., 1889 (116), 64. 

 3 Ziegler's Beitr., 1900 (28), 541. 4 Pfliiger's Arch., 1896 (63), 209. 



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



