CHAPTER XXI. 



ATROPHY. 



ATROPHY is a diminution in the size of a part, due to a deficient 

 nutrition of its constituents, which is neither so rapid nor so destruc- 

 tive as to cause necrotic, degenerative, or inflammatory changes. 

 The tissue-elements appear comparatively normal under the micro- 

 scope, but are either all or in part diminished in size. This dimi- 

 nution in size is frequently accompanied by an increased depth of the 

 usual coloring of the tissue-elements, or with th'e appearance of 

 granules of pigment (Fig. 256). 



FIG. 256. 



Brown or senile atrophy of the heart. (Ribbert.) The muscle-fibres are reduced in diameter. 

 At the ends of the nuclei are collections of pigment-granules. 



The cause of atrophy may operate almost directly upon the cells 

 involved, or it may indirectly influence the nutrition of the cells 

 through lesions in the circulatory or nervous system, or through an 

 interference with the processes of general nutrition maintaining the 

 whole body. 



1. Functional Atrophy. It appears to be a general principle gov- 

 erning living organisms that functional activity, within a certain 

 normal range, is necessary to the maintenance of the normal nutri- 

 tion of a part. When the required degree of functional activity 

 is not called forth, the nutrition of the part suffers and it undergoes 

 atrophy. Paralyzed muscles lose their normal size through innutri- 

 tion following their disuse. Secreting glands may also suffer atrophy 



284 



