THE SYMPATHETIC NERVOUS SYSTEM. 631 



centripetal nerve, as when cold is applied to the skin, then the impres- 

 sions are reflected so as to produce movements which, though they may 

 be very quick and almost convulsive, are yet combined in the plan of the 

 proper respiratory acts. 



Among the ganglia of the sympathetic nerves to which this co-ordi- 

 nation of movements is to be ascribed, must be reckoned those which lie 

 in the very substance of the organs; such as those of the heart. Those 

 also may be included which have been found in the mesentery close by 

 the intestines, as well as in the muscular and submucous tissue of the 

 stomach and intestinal canal, and in other parts. 



Respecting the influence of the sympathetic system on the various 

 physiological processes, the sections on the Heart, Arteries, Animal 

 Heat, Salivary Glands, Stomach and Intestines should be referred to. 



Influence of the Nervous System in general on Nutrition. It 

 has been held that the nervous system cannot be essential to a healthy 

 course of nutrition, because in plants, in the early embryo, and in the 

 lowest animals, in which no nervous system is developed, nutrition goes 

 on without it. But this is no proof that in animals which have a ner- 

 vous system, nutrition may be independent of it; rather, it may be 

 assumed, that in ascending development, as one system after another is 

 added or increased, so the highest (and, highest of all, the nervous sys- 

 tem) will always be present and blended in a more and more intimate 

 relation with all the rest: according to the general law, that the inter- 

 dependence of parts augments with their development. 



The reasonableness of this assumption is proved by many facts show- 

 ing the influence of the nervous system on nutrition, and by the most 

 striking of these facts being observed in the higher animals, and espe- 

 cially in man. The influence of the mind in the production, aggravation, 

 and cure of organic diseases is matter of daily observation, and a sufficient 

 proof of influence exercised on nutrition through the nervous system. 



Independently of mental influence, injuries either to portions of the 

 nervous centres, or to individual nerves, are frequently followed by 

 defective nutrition of the parts supplied by the injured nerves, or deriv- 

 ing their nervous influence from the damaged portions of the nervous 

 centres. Thus, lesions of the spinal cord are sometimes quickly followed 

 by gangrene of portions of the paralyzed parts. After such lesions also, 

 the repair of injuries in the paralyzed parts may take place less com- 

 pletely than in others; as, in a case in which paraplegia was produced 

 by fracture of the lumbar vertebrae, and, In the same accident, the 

 humerus and tibia were fractured. The former in due time united: the 

 latter did not. The same fact was illustrated by some experiments, in 

 which having, in salamanders, cut off the end of the tail, and then 

 thrust a thin wire some distance up the spinal canal, so as to destroy the 

 cord, it was found that the end of the tail was reproduced more slowly 



