NECROSIS 371 



dyes which cannot penetrate hvinj; cells may stain dead or dying cells.'* 

 These changes depend on alterations in permeability, and as permea- 

 bility determines electrical resistance, Osterhout has used the resistance 

 of plant cells as an indicator of vitality. He finds that normal cells 

 have a rather constant resistance, which is reduced by anything that 

 lowers the vitality' of the cell, and in direct proportion to the degree 

 of injur}' or loss of vitality.'^ The temperature coefficient is also 

 considerablj' lower in dead than in living tissue. ^^ When secondarj' 

 disintegrative changes occur in the protoplasm, with the formation of 

 many small molecules from the large molecules of the cell, both osmo- 

 tic pressure and electrical conductivity increase rapidly. Changes 

 in the permeability of cell protoplasm, however, may be of considerable 

 degree without necessarily^ indicating serious injury of the cells (Oster- 

 hout).^^ Death is accompanied by changes of the character of a 

 monomolecular reaction, which is continually going on and w'hich is 

 accelerated by the toxic agent. '^ Up to a certain point the reaction 

 seems to be reversible. 



A principle of colloid chemistry, the alteration of colloids with time, has an 

 interesting bearing on the question of aging and natural death of tissues.'*" It 

 is characteristic of colloidal solutions (which, of course, is what cells are), that 

 they continuously change in their properties, the change being generally in the 

 direction of aggregation of the disperse colloidal particles, with a resulting ten- 

 dency to precipitation or coagulation; the gels tend to decrease in elasticity and 

 to become more turbid, associated with which are alterations in their perme- 

 ability to crystalloids. A gelatin mass possesses its maximum elasticity three 

 or four hours after it is first formed; and crystalloids penetrate fresh, quickly- 

 formed gels at first more rapidly than later. As Bechhold says, we can imagine 

 (1) a relation of such facts to the greater elasticity of young tissues; (2) to a pre- 

 sumably greater permeability for crystalloids and hence more rapid metabolism; 

 (3) to the decreasing water of the tissue with age (94 per cent, of water in the 

 fetus of three months, 69-66 per cent, at birth, and 58 per cent, in adults); (4) 

 to the demonstrated greater permeability of young nerve tissues for vital stains, 

 etc. "In general we can say that the tissue colloids decrease in their water affinity 

 (Quellbarkeit) both in animal organisms, which become poorer in water with age, 

 and in plants, as shown by the hardening of older plant tissues." The bearing 

 of these principles on the problem of senility and degeneration of elastic tissue, 

 regeneration and many other subjects is obvious. 



Causes of Necrosis 



Anemia. — After the cutting off of blood-supply, cells soon undergo 

 morphological changes that we recognize as indicating their death, and 

 after a time they also become incapable of returning to their normal 

 condition when the blood-supply is re-established, probably because 

 of these structural changes. In just what way lack of nourishment 



" See Steckelmacher, Beitr. path. Anat., 1913 (57), 314. 



15 See Science, 1914 (40), 488. 



1^ Galeotti's earher observations with animal tissues (Zeit. f. Biol., 1903 (45), 

 65) do not harmonize with Osterhout'fe results, and Galeotti's idea that there is a 

 special degree of ionization characteristic of living cells is not established. 



1^ Botan. Gaz., 1915 (59), 242. 



18 Osterhout, Jour. Biol. Chem., 1917 (31;, 585. 



18" See H. Bechhold, "Die Kolloide in Biologic und Medizin," Dresden, 1912, 

 „• 65. 



