CHAPTER XV 



RETROGRESSIVE CHANGES (NECROSIS, GANGRENE, RIGOR 

 MORTIS, PARENCHYMATOUS DEGENERATION) 



NECROSIS 



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

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

 at the 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 physi- 

 cally, and exhibits no chemical activity, yet it is by no means dead, 

 since it still possesses the latent power to assume again an active exist- 

 ence under suitable conditions. In pathological conditions we are 

 accustomed to recognize the fact that a cell is dead by certain altera- 

 tions in its structural appearance, particularly disintegrative 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 ab- 

 solutely 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 postmortem decomposition by embalm- 

 ing. For example, if we examine microscopically the mucous mem- 

 brane of the stomach of a person who has died immediately after 

 taking a large quantity 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 un- 

 changed 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 ordinary 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 may be very difficult to determine always whether a cell is 

 dead or not. Part of the difficulty, perhaps, hes in our failure to 

 appreciate that not all parts of a cell die at the same time; i. e., the 

 different chemical processes of the cell depend on its different intracell- 

 ular enzymes, and these are not necessarily destroyed alike by the 

 same agents. Even considerable respiratory activity may be ex- 

 hibited by cells that have been killed.^" 



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

 cells of its body do not die for some time as shown by the following 



i^See Haas, Bot. Gazette, 1919 (67), 347. 



367 



