382 RETROGRESSIVE CHANGES 



in the acid reaction of the part involved (Chambers) ^^ and Hkewise 

 traumatized nervous tissues develop an acid reaction (Moore). ^^ 

 Many lower animals devoid of a nervous system respond to mechanical 

 stimuli by chemical activity; e. g., the production of phosphorescence 

 by marine organisms when agitated by an oar, etc. Possibly, the 

 secretion of thrombokinase by the leucocytes, which occurs whenever 

 they come in contact with a foreign body, is an example of a similar 

 reaction to a mechanical stimulus. Even in urticaria factitia the sim- 

 ple mechanical irritation which suffices to produce the wheals is fol- 

 lowed very quickly by extensive nuclear fragmentation,^^ but it may 

 be that unknown poisons are present in the hypersensitive skin and 

 cause the karyorrhexis, and not the trauma alone. We have no good 

 evidence that mere contact with a chemically inert foreign body unac- 

 companied by cellular injury, can cause death of tissue-cells.^^ How- 

 ever, Chambers ^^" states that simple trauma, even mere compression, 

 of the eggs of asteria may cause them to coagulate into a solid mass. 

 Extreme changes in osmotic pressure may lead to cell death, either 

 by causing structural alteration in the cell (e. g., the bursting of plant- 

 cells in water), or concentration of the electrolytes may become so 

 great that the colloids are thrown out of solution, as in the ordinary 

 salting-out processes of the laboratory. It is doubtful, however, if 

 osmotic changes per se ever become so abnormal within the animal 

 body (except in experimental conditions) as of themselves to cause cell 

 necrosis. 



Varieties of Necrosis 



Coagulation Necrosis.' — This name is applied to necrotic areas 

 that are firm, dry, usually pale yellowish in color, and observed prin- 

 cipally in areas of total anemia or tuberculosis. The question has 

 been long disputed as to whether a true coagulation occurs in such 

 tissues or not. Necrosis produced by heat, carbolic acid, corrosive 

 sublimate, etc., is naturally a coagulation necrosis, the cells of the 

 affected area having undergone true coagulation; i. e., the conversion 

 of their soluble colloids (sols) into the insoluble "pedous" modification. 

 Whether the same change occurs in areas of anemic necrosis is not so 

 well established. If the part contains a fair amount of plasma the 

 liberation of the tissue coagulins from the dead cells will cause a con- 

 version of the fibrinogen into fibrin — this can usually be demonstrated 

 microscopically, but the presence of fibrin is not constant, and its 

 quantity is usually insufficient to explain satisfactorily the condition 



»« Amer. Jour. Physiol., 1917 (43), 1. 

 " Proc. Soc. Exp. Biol. Med., 1917 (15), 18. 

 08 Gilchrist, Bull. Johns Hopkins Hosp., 1908 (19), 49. 



90 Meltzer (Zeit. f. Biol., 1894 (30), 4G4) has shown that bacteria may be 

 killed by violent agitation, which causes disintegration of the cells. 

 09" Trans. Roy. Soc. Canada, 1918, p. 41. 

 ^ Literature by Jores, Ergebnisse der Pathol., 1898 (5), IG. 



