374 RETROGRESSIVE CHANGES 



and Uschinsky^^ noted that in animal tissues the nuclei were less af- 

 fected b}^ cold than the cytoplasm. Blood seems little affected by 

 freezing temperature, for du Cornu found that dog's blood kept on 

 ice for five to ten days could be employed for transfusion without 

 causing hemoglobinuria. Grawitz saw motion persist in human cili- 

 ated epithelium kept for seven to nine days on ice. Cihated epi- 

 thelium 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 freez- 

 ing depends not so much upon the freezing of the cells themselves as 

 upon the formation of hyalin thrombi in the injured vessels (v. Reck-j 

 linghausen, Hodara).^^ Kriege^'' found that if the freezing is transi- 

 tory, the thrombi may again disappear; if over two hours in duration, 

 they are persistent. Rischpler,^^ however, considers that cell death 

 is due primarily to the effect of the cold upon the cells, and Lake^- 

 found that for both isolated cells in culture and living tissues with 

 intact blood supply, deai.b occurred at —6° C, this being the tempera- 

 ture at which protoplasm freezes. On the other hand, Steckel- 

 macher^^" found that freezing of liver tissue produced the same changes 

 as ligation of the hepatic artery, i. e., increased permeabiHty of the 

 cell wall followed by similar changes in the nucleus, suggesting that 

 the changes produced by freezing depend on the vascular changes. 



Light.^'^ — ^Light may affect tissues seriously, apart from the effects 

 of accompanying heat, although the experiments of Aron^^ indicate 

 that insolation does not depend on the light raj^s, but solely on the 

 heat. In the treatment of lupus by the Finsen method with concen- 

 trated light rays, the action is largely a stimulating one, but associ- 

 ated with or subsequent to a certain degree of cell injury. Ogneff^^ 



" Ziegler's Beitr., 1893 (12), 115. 



^8 In plant cells it is the freezing and not the thawing that causes the harm 

 (Maximow, Berichte Deut. Bot. Gesell., 1912 (30), 50-4). 



29 Miinch. med. Woch., 1896 (43), 341. 



30 Virchow's Arcli., 1889 (116), 64. 

 " Ziegler's Beitr., 1900 (28), 541. 

 32 Lancet, Oct. 13, 1917. 



32" Beitr. path. Anat., 1913 (57), 314. 



" Review by Bering, Ergeb. allg. Pathol., 1914, Abt. 1 (17), 790. See dis- 

 cussion of the principles of the action of light on tissues by Bovie, Anier. Jour. 

 Tropical Dis., 1915 (2), 506. 



•"• PliiU])i)ine Jour. Sci., B, 1911 (6), 101. 



a' Pfiiiger's Arch., 1896 (63), 209. 



