ATROPHY, DEGENERATION, PIGMENTATION, AND NECROSIS. 89 



be deposited iu the liver and elsewhere in the form of yellow or brown 

 granules. 



METABOLIC PIGMENT. Pigment may be elaborated by various forms 

 of cells by processes apparently somewhat analogous with those con- 

 cerned in normal pigmentation. 1 This is exemplified in melanotic 

 tumors, most frequently of the choroid and the skin, and possibly in the 

 bronze skin of Addison's disease. 



Pigment whose nature is not very clearly defined may form in the 

 smooth muscle tissue of the gastrointestinal walls, in various cachexire, 

 in the heart muscle, in the so-called "brown atrophy," and, under certain 

 conditions, in the liver. 



As examples of pigment introduced into the body from without, we 

 may mention the deposition of minute particles of silver from the inter- 

 nal use of silver salts argyria ; the coloring of the skin and lymph 

 glands from tattooing ; and especially the pigmentation of the lungs and 

 bronchial glands from the inhalation of coal and other dnst^-pneumono- 

 koniosis (Fig. 26). This is universally present under the conditions of 



FIG. 26. PIGMENTATION OF CONNECTIVE-TISSUE CELLS OF THE LUNGS. 

 From inhaled coal dust anthracosis. 



indoor life which modern civilization imposes. Such pigment may be 

 brown or black, and is usually in very small particles within cells or in 

 the intercellular stroma. 



Necrosis. 



Necrosis is the death of a circumscribed portion of tissue. It may 

 be the result of insufficient nutrition, from the cutting off of the blood 

 supply; or it may depend upon the action of destructive chemical 

 agents, extreme degrees of temperature, certain materials produced by 

 the life processes of some forms of bacteria ; or it may be due to me- 

 chanical injury. The general appearance of dead tissues varies greatly. 

 In some cases there is a simple and gradual disintegration and softening 



'For a study of the nature of skin pi 

 Experimental Medicine, vol. i., p. 361, 188 

 Journal of Physiology, vol. ii., p. 291, 1899. 



jment, consult Abel and Davis, Journal of 

 >; also Chittenden and Albro, American 



