CHAPTER XIII 



RETROGRESSIVE CHANGES (NECROSIS, GAN- 

 GRENE, RIGOR MORTIS, PARENCHYMATOUS 

 DEGENERATION) 



NECROSIS 



WE recognize that a cell is alive through its reproducing, 

 functionating, and its taking on and utilizing nutritive sub- 

 stances ; yet at the same time we appreciate that a cell may do 

 none of these things and still be alive. For example, a bac- 

 terial 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 again assume an active existence under suitable 

 conditions. In pathological conditions we are accustomed to 

 recognize the fact that a cell is dead by certain alterations 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 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 postmortem decomposition by embalming. For example, 

 if we examine microscopically the mucous membrane 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 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 ordinary histo- 

 logical 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, lies in our failure to appreciate 



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