- SECTION IX 



TROPHIC FUNCTIONS OF THE CORD 



THE reflexes which are excited by painful or nocuous stimuli must be 

 regarded as prepotent in that their inhibitory effect on other reflexes is 

 more marked than that produced by any other quality of stimulus. In the 

 struggle for existence the reaction to nocuous stimuli must predominate over 

 those due to any other kind, since it is essential for the survival of the animal 

 that the stimulus should be removed or avoided, so that the animal should 

 escape from its injurious effects. 



It is natural therefore that after complete section of the afferent nerves 

 from any part of the surface of the body there should be a tendency ,to 

 trophic disturbances, such as the formation of ulcers, &c. Such ulceration is 

 frequently observed in patients suffering from spinal disease. After section 

 of the first division of the fifth nerve ulceration of the cornea is of ten produced. 

 These effects are however merely due to the absence of the normal protective 

 reactions of the part, and can be prevented by scrupulous cleanliness and 

 protection of the apaesthetic part from all possible injuries. There are other 

 trophic effects caused by nerve lesions which cannot be ascribed to the mere 

 absence of protective reflexes. Thus inflammation of the posterior root 

 ganglia often sets up herpes zoster, or ' shingles,' in the region of cutaneous 

 distribution of the corresponding sensory nerve. Changes in the skin ( ' glossy 

 skin ') nails and hair are often seen after irritative injuries of nerves to the 

 part. Section of a motor nerve causes rapid changes in the skeletal muscles 

 supplied, which become smaller and after months or years may disappear 

 altogether, being replaced by connective tissue. The changes in the excita- 

 bility of the muscles produced under these circumstances have already been 

 described. 



It seems that the nutrition of a tissue is determined by its activity, and 

 this in turn is under the control of some nerve path. Section of the nerve 

 path, by cutting away the impulses which normally maintain the activity of 

 the part, must at the same time seriously affect its nutrition. Thus the 

 muscles which, though striated, are not so immediately under the control 

 of the central nervous system, such as the sphincter ani, do not undergo 

 degeneration after section of their nerves, or after extirpation of the lower 

 part of the spinal cord. 



On the other hand, it is only during post-foetal life that the activity of 

 the skeletal muscles is determined by the motor nerves of the cord. Thus 



349 



