ATEOPHY AND DEGENERATIONS OF TISSUE. 53 



the whole organ. Muscular tissue also wastes in tlie same way, 

 by a decrease in the size of the primitive fasciculi, as exemplified 

 in the voluntary muscles and the heart. 



Numerical atrophy resembles gangrene in some respects, for 

 death of the part is common to both ; but they differ in the 

 following points. In gangrene, tracts of tissue are affected. It 

 results from some sudden arrest of nutrition, and a gangrenous 

 mass remains at the termination of the process, in such a condi- 

 tion that the structure can be usually recognised ; whereas in 

 necrobiosis^ the change is a molecular one, with gradual ex- 

 haustion of the vital power, a molecular disintegration and 

 destruction of elements, so that at the termination of the process 

 all that remains is a glandular debris, in wliicli no trace of the 

 natural structure of the part can be discovered. This form of 

 atrophy is of much greater importance than the simple ; for in 

 the simple the elements of the part continue to exist, and 

 repair can be effected without any new formation ; whilst in the 

 numerical, restitution is only possible by the production of new 

 elements. 



Inactivity of a part, obstruction of its blood-vessels, failure of 

 its own vital energy, continued pressure upon its surface, and 

 the process of inflammation, are all well-known causes of atrophy. 

 A muscle, if unused, becomes small and pale, and its tissue 

 degenerates. This atrophy of muscular tissue from diminished 

 activity is often seen in the horse. For example, a horse is 

 chronically lame in a foot. In consequence of tlie pain felt by 

 the animal, the limb is kept in a state of quietude and repose ; 

 the animal moves it as little as possible. The muscles, thus 

 kept inactive, diminish in size, and the whole limb seems to 

 shrink. If the cause of the lameness be removed, and the limb 

 regain its former activity, the wasted muscles are restored to 

 their natural condition and strength. Paralysis also leads to 

 shrinking of a limb ; and- it is recorded that injury to a trunk of 

 the sympathetic nerve will produce the same condition without 

 impairment of motion or sensibility. Atrophy and softening 

 may result from the ingestion of improper food. Majendie kept 

 animals upon food containing no nitrogen and incapable of 

 supplying sufficient nourishment ; and one curious result was 



^ The term necrobiosis is applied by Virchow to the destruction of histological 

 elements, which occurs both in atrophy and degeneration. 



