CAUSES OF NECROSIS 373 



may be more susceptible to heat than under other conditions. Just 

 how coagrulation of cell o-lobulins can determine the deatli of a cell 

 is difficult to understand, unless the physical conditions of the cell 

 are jjreatly altered thereby. Ordinarily we have in the cell an equi- 

 librium between colloids in solution and colloids in the solid or gel 

 state; if the colloids are rendered insoluble by heat, or by any other 

 cause, so that this equilibrium is destroyed, serious alterations in the 

 mechanism of all metabolism must result (Mathews). Other chem- 

 ical reactions will also have their point of equilibrium altered by 

 clian<>es in temperature, and such .alterations miglit well have disas- 

 trous results. 



Different tissues show unequal susceptibility to heat. Werhov- 

 sky ^^ found the blood most affected by raising the temperature of 

 living animals, next the liver, kidneys, and myocardium in order, 

 the other tissues being little or not at all structurally injured. 



Cold is well withstood by unicellular forms, and relatively poorly 

 by more complex organisms, particularly by those with a highly de- 

 veloped circulatory system ; this is because individual cells are not 

 greatly affected by freezing, whereas the circulatory channels are 

 readily blocked by this cause. Bacterial cells are not killed by ex- 

 posure for long periods to the temperature of liquid air ^^ ( — 190°). 

 Reduction of the temperature of plant cells to — 13° may result in 

 a granular transformation of the cytoplasm, often with rather seri- 

 ous structural alterations. Cytoplasm seems to be more affected than 

 the nucleus, for mitosis may occur slowly in plant cells at — 8°, 

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

 fected by 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. Ciliated 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 bj^ the subsequent 

 thawing, are sufficient to render them incapable of further exist- 

 ence.-'' Cells devoid of or poor in water cannot be killed by freez- 

 ing, 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- 



i7Ziegler's Beitr., 1895 (18), 72. 

 isMacFadven, Lancet. 1900 (i), 849. 

 i9Ziegler's Beitr., 1893 (12), 115. 



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

 (Maximow, Berichte Deut. Bot. Gesell., 1912 (30), 504). 



