PRINCIPLES OF VETERINARY SURGERY 83 



are not atrophies. The use of the word "atrophy" must be 

 restricted to the wasting process in which the normal consti- 

 tution of the part is fairly well maintained. When a degen- 

 erative, process predominates the phenomenon is not an 

 atrophy. 



In the simple atrophy commonly encountered in domestic 

 animals the affected part exhibits a dearth of cells and a 

 manifest diminution in their size, while the intercellular sub- 

 stance remains unchanged. The loss of volume is due strictly 

 to this behavior oi the cellular elements. 



The causes of local atrophies are: (i) Peripheral par- 

 alysis, (2) inactivity or disuse, (3) pressure, and (4) centric 

 paralysis. 



(i) Peripheral Paralj^is. — When a nerve-trunk supply- 

 ing the motor innervation of a part is bruised, compressed, 

 violently stretched, or divided, a wasting process will super- 

 vene. In the case of muscles where the normal volume de- 

 pends upon their activity, the wasting process may be excep- 

 tionally rapid, if the motor innervation is wanting. A muscle 

 made perfectly vapid by impairment of its motor nerve will 

 shrink much more rapidly than inactive muscles normally 

 supplied with nerves. Whether this difference is due to the 

 absence of trophic influences or not, cannot easily be deter- 

 mined because absolute inactivity of normal muscles seldom 

 ever exists. The very rapid wasting of certain muscles of 

 the horse after their motor nerve is injured would, however, 

 indicate that inactivity is not alone responsible, but that 

 some other causative factor enters into the process. 

 Whether this subtile influence is failure of the trophic inner- 

 vation, thrombosis, or local vaso-motor disturbance, is diffi- 

 cult to decide. 



There are three special examples of atrophy from peri- 

 pheral paralysis in the horse, that beggar description from 

 this standpoint. These are: (i) Atrophy of the external 



