380 RETROGRESSIVE CHANGES 



and the toxicity of a salt is a function of the sum of the toxicity 

 of the ions; hence the toxicity of a salt is in inverse proportion to 

 its decomposition tension. Kunkel suggests that oxalic acid and 

 fluorides are poisons because they combine the cell calcium, and 

 barium salts may be poisonous because they precipitate the SO4 ions. 

 We can readily imagine that the combining of even one of the essential 

 constituents of the cell may so upset the normal chemical processes 

 that the cell can no longer take up substances to repair its waste, and 

 hence necrosis ensues.^^ 



Physical agents may cause necrosis, usually in ways too obvious 

 to require explanation. With most cells, large portions of the cyto- 

 plasm can be destroyed without serious results, for so long as the 

 nucleus is intact the cytoplasm can be reconstructed. The fact that 

 necrosis frequently follows relatively slight injuries of the nucleus 

 is perhaps best explained by considering that injury to the nuclear 

 membrane modifies the permeability of the nucleus for substances in 

 solution, which might readily affect its metabolic activities to a serious 

 degree. It is possible, also, that solvents of lipoids, such as chloro- 

 forai, etc., produce much of their deleterious effects by modifying 

 the permeability of the cell, if the semipermeability of cell mem- 

 branes depends largely upon the lipoids they contain."* 



Physical injury of even slight degree may bring on severe alterations 

 in cells, however, and indeed may cause severe chemical alterations. 

 We know that many chemical reactions can be brought about by slight 

 mechanical disturbances, e. g., the explosion of fulminate, nitrogen 

 iodide, etc., and it is quite possible that mechanical disturbances can, 

 likewise, cause chemical changes in the protoplasm. ]\Ian3^ 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. Possibh% the secre- 

 tion of thrombokinase by the leucocytes, which occurs whenever they 

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

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

 ple mechanical irritation which suffices to produce the wheals is 

 followed 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 uiuic- 

 com]ianied by cellular injury, can cause death of tissue-cells."" 



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



«3 It is hardly profitablo here to go further into tlie theories of the aetion of 

 poisons, which are generally extensively considered in the treatises on toxicology 

 and pharmacology (also by Davenport, loe. cit.) . 



"4 See I'ascncci*. Tlofmeister's IJeitriigc, 190") (0), ,'552. 



"r- Gilchrist, Bull. Johns Hopkins Tlosp., 1008 (19), 49. 



•■■"Meltzer (Zeit. f. Riol., 1894 (.30), 4(14) has shown tliat bacteria may be 

 killed by violent agitation, whicli causes disintegration of tlie cells. 



