308 NUTRITION. 



itself on every side : a striking instance how, from the same 

 source, many tissues maintain themselves, each exercising its 

 peculiar assimilative and self-formative power. 



3. The third condition said to be essential to a healthy nu- 

 trition, is a certain influence of the nervous system. 



It has been held that the nervous system cannot be essential 

 to a healthy course of nutrition, because in plants and 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 nervous system, nutri- 

 tion 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 

 system) will always be inserted and blended in a more and 

 more intimate relation with all the rest: according to the 

 general law, that the interdependence of parts augments with 

 their development. 



The reasonableness of this assumption is proved by many 

 facts showing the influence of the nervous system on nutrition, 

 and by the most striking of these facts being observed in the 

 higher animals, and especially in man. The influence of the 

 mind in the production, aggravation, and cure of organic dis- 

 eases 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 por- 

 tions of the nervous centres, or to individual nerves, are fre- 

 quently followed by defective nutrition of the parts supplied 

 by the injured nerves, or deriving their nervous influence from 

 the damaged portions of the nervous centres. Thus, lesions of 

 the spinal cord are sometimes followed by mortification of por- 

 tions of the paralyzed parts ; and this may take place very 

 quickly, as in a case by Sir B. C. Brodie, in which the ankle 

 sloughed within twenty -four hours after an injury of the spine. 

 After such lesions also, the repair of injuries in the paralyzed 

 parts may take place less completely than in others ; so, Mr. 

 Travers mentions 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 of Dr. Baly, in which having, in salaman- 

 ders, 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, he 

 found that the end of the tail was reproduced more slowly than 

 in other salamanders in whom the spinal cord was left unin- 

 jured above the point at which the tail was amputated. Illus- 

 trations of the same kind are furnished by the several cases in 



