CHAPTER XIII 



RETROGRESSIVE CHANGES (NECROSIS, GANGRENE, 

 RIGOR MORTIS, PARENCHYMATOUS DEGENERA- 

 TION) 



NECROSIS 



We recognize that a cell is alive through its reproducing, func- 

 tioning, and its taking on and utilizing nutritive substances; yet 

 at tlie same time we appreciate that a cell may do none of these things 

 and still be alive. For example, a bacterial spore is quite inert 

 physically, and exhibits no chemical activity, yet it is by no means 

 dead, since it still possesses the latent power to assume again an 

 active existence under suitable conditions. In pathological condi- 

 tions we are accustomed to recognize the fact that a cell is dead by 

 certain alterations in its structural appearance, particularly disin- 

 tegrative changes in the nucleus ; but this is exactly equivalent to 

 recognizing that an animal is dead by the appearance of postmortem 

 decomposition, for most of the characteristic histological changes of 

 necrosis are merely postmortem changes in the cell. A cell may be 

 dead and show absolutely none of these microscopic disintegrative 

 changes, either because it has not been dead long enough for them 

 to have taken place, or because the changes have been prevented 

 by some means, just as we can prevent the appearance of postmor- 

 tem decomposition by embalming. For example, if we examine mi- 

 croscopically the mucous membrane of the stomach of a person who 

 has died immediately after taking a large ([uantity of carbolic acid, 

 although to the naked eye this mucous membrane is hard, white, 

 and definitely necrotic, yet we find the histological picture presented 

 by the cells almost absolutely unchanged from the normal. The 

 cells are dead, but they have been so "fixed" that postmortem 

 changes could not affect their structure. All cells examined by ordi- 

 nary histological methods are, of course, dead — killed by the fixing 

 agents outside of the body, in the same way that the carbolic acid 

 fixes them within the body. It is evident, therefore, that it ma.v be 

 very difficult to determine always whether a cell is dead or not. Part 

 of the difficulty, perhaps, lies in our failure to appreciate that not all 

 parts of a cell die at the same time; i. e., the causes of different chem- 

 ical processes of the cell reside in its different intracellular enzjones, 

 and these are not necessarily destroyed alike by the same agents. 



AVe recognize that after an animal is dead as a whole the various 



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