612 A MANUAL OF PHYSIOLOGY 



changes. In the paralyzed muscles nutrition is not only 

 interfered with in consequence of their inactivity, as would 

 be the case even if the paralysis were due to a lesion above 

 the level of the anterior cornual cells, but the already poorly 

 nourished fibres are continually pressed upon by the capil- 

 laries, which are dilated owing to the division of the vaso- 

 motor nerves. The degeneration must also be in part ascribed 

 to the loss of a tonic influence exerted on the muscles by the 

 motor cells of the spinal cord, through the ordinary motor 

 serves (p. 713). 



Section of the cervical sympathetic in young rabbits and 

 dogs is said to increase the growth of the ear and of the 

 hair on the same side ; but it is impossible to separate these 

 consequences from the vaso-motor paralysis ; and the same 

 is true of the hypertrophy following section of the vaso- 

 motor nerves of the cock's comb and of the nerves of bones. 

 The statement has been made that on section of the superior 

 laryngeal nerve in the horse the laryngeal muscles on the 

 corresponding side undergo rapid atrophy. Since the nerve 

 in this animal is destitute of motor fibres this seemed to 

 indicate either that the nerve contains efferent * trophic ' 

 fibres for the muscles, or that the activity of its afferent 

 fibres has a profound influence on their nutrition. But by 

 means of the laryngoscope it has been shown that after 

 section of the superior laryngeal the vocal cord on the side 

 of the section is at once rendered motionless, and remains 

 so. The atrophy of the muscles is therefore due to their 

 inaction in the absence of the sensory impulses by which 

 the centre controlling them is normally roused to activity. 

 And Mott and Sherrington have found that, although section 

 of the posterior roots in monkeys is followed after a. time 

 (three weeks to three months) by ulceration over certain 

 portions of the foot, no corresponding lesions occur in the 

 hand. They believe, therefore, that the lesions are not due 

 to the withdrawal of a reflex trophic tone, but are accidental 

 injuries in positions specially exposed to mechanical or 

 microbic insults. 



Omitting the group of ' trophic ' nerves, and the even 

 more problematical * thermogenic ' fibres (which some have 



