90 



ATROPHY, DEGENERATION, PIGMENTATION, AND NECROSIS. 



of the tissue, resulting in a mass of degenerated cells and cell detritus, 

 with more or less fluid and various chemical substances arising from de- 

 composition. The softening of the brain in embolism is an example of 

 simple uecrotic softening. In some cases the dead tissues merely grad- 

 ually dry and shrivel and become hard and dark colored. 



In another class of cases the dead tissues are permeated by fluids 

 which may be dark red in color, from the solution of coloring matter 

 from the blood, and may contain bacteria which induce putrefaction, with 

 the production of gases and various new chemical substances. The tissues 

 become swollen and granular, and disintegrate; and finally the whole 



FIG. 37.- NECROSIS OF EPITHELIUM IN THE KIDNEY. 



The cells in the lower portion of the cut are nearly normal ; most of those above are more coarsely granu- 

 lar and have failed to take the nuclear stain, while at the top they are disintegrating. 



may form a mass of irregular granules, with fat droplets, tyrosin, leucin, 

 and various forms of crystals, shreds of the more resistant kinds of tis- 

 sue, and bacteria. 



There is at first no evident morphological difference between dead 

 cells and living cells. But very soon in the former, secondary changes 

 occur. The cytoplasm becomes more coarsely granular. The nucleus 

 stains less deeply or not at all with hsematoxylin or other nuclear 

 dyes (Fig. 27), owing to the disappearance of the chromatiii which 

 seems to dissolve in the tissue juices; this is called karyolysis. Some- 

 times, however, the chromatiii only partially disappears, the remainder 

 breaking up into irregular, more or less deeply staining granules. This 

 is called Itaryorrhexis. Presently the cell body may contain fat droplets, 

 or without this it may disintegrate. 



GANGRENE. When death of a considerable mass of tissue occurs, and 

 this either dries, as is possible on the surface of the body, or is associated 

 with putrefaction in the tissue, the condition is called gangrene. The 

 involved part, when on the surface of the body, may dry and become 



