NECROSIS 373 



norve-cells. This fact is undoubtedly of great practical importance 

 in causing death from fever, for although 47° C. (117° F.) is prob- 

 ably never reached in man, yet application of much lower tempera- 

 tures, even 42° (108° F.), for a few hours will cause coagulation of 

 these proteins (all proteins coagulate at less than their ordinary 

 coagulation point if the heating is continued for a long time). It 

 would seem from the above observation that heat may cause cell death 

 through coagulation of the proteins. Whether the cell death is in 

 any way dependent upon destruction of the enzymes by heat has not 

 l)een ascertained; but as most enzymes are not destroyed nmch be- 

 low 60°-70°, it seems impro})able that they are greatly injured at 

 the temperatures at which cells are killed. It is possible, however, 

 that under the conditions in which enzymes exist in the cell they 

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

 how coagulation of cell globulins can determine the death of a cell 

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

 are greatly 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 equihbrium altered by 

 changes in temperature, and such alterations might 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. Ani- 

 mals exposed to heat show a fall in the leucocyte count, followed by a 

 rise in lymphocytes which persists; there is an extensive degeneration 

 of cells in the spleen and lymph glands, followed by marked mitotic 

 proliferation in the germinal centers. ^^ 



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°, 



2* Ziegler's Beitr., 18P5 (18), 72. 



" Murphy and Sturm, Jour. Exp. Med., 1919 (29),- 1. 



-^* Sy:^temic rffectsof cold reviewed by Foord, Jour. Infect. Dis., 1918(23), 159. 

 2 MacFadyrn, Lan et, 1900 (i), 849. 



