INFLUENCE OF NERVOUS SYSTEM. 309 



which division or destruction of the trunk of the trigeminal 

 nerve has been followed by incomplete and morbid nutrition 

 of the corresponding side of the face; ulceration of the cornea 

 being often directly or indirectly one of the consequences of 

 such imperfect nutrition. Part of the wasting and slow de- 

 generation of tissue in paralyzed limbs is probably referable 

 also to the withdrawal of nervous influence from them; though, 

 perhaps, more is due to the want of use of the tissues. 



Undue irritation of the trunks of nerves, as well as their 

 division or destruction, is sometimes followed by defective 

 or morbid nutrition. To this may be referred the cases in 

 which ulceration of the parts supplied by the irritated nerves 

 occurs frequently, and continues so long as the irritation lasts. 

 Further evidence of the influence of the nervous system upon 

 nutrition is furnished by those cases in which, from mental an- 

 guish, or in severe neuralgic headaches, the hair becomes gray 

 very quickly, or even in a few hours. 



So many and various facts leave little doubt that the ner- 

 vous system exercises an influence over nutrition as over other 

 organic processes ; and they cannot be explained by supposing 

 that the changes in the nutritive processes are only due to the 

 variations in the size of the bloodvessels supplying the affected 

 parts. 



The question remains, through what class of nerves is the 

 influence exerted? When defective nutrition occurs in parts 

 rendered inactive by injury of the motor nerve alone, as in the 

 muscles and other tissues of a paralyzed face or limb, it may 

 appear as if the atrophy were the direct consequence of the 

 loss of power in the motor nerves ; but it is more probable that 

 the atrophy is the consequence of the want of exercise of the 

 parts ; for if the muscles be exercised by artificial irritation of 

 their nerves their nutrition will be less defective (J. Reid). 

 The defect of the nutritive process which ensues in the face 

 and other parts, moreover, in consequence of destruction of the 

 trigeminal nerve, cannot be referred to loss of influence of any 

 motor nerves; for the motor nerves of the face and eye, as well 

 as the olfactory and optic, have no share in the defective nu- 

 trition which follows injury of the trigeminal nerve ; and one 

 or all of them may be destroyed without any direct disturbance 

 of the nutrition of the parts they severally supply. 



It must be concluded, therefore, that the influence which is 

 exercised by nerves over the nutrition of parts to which they 

 are distributed is to be referred either to those among their 

 branches which conduct impressions to the brain and spinal 

 cord, namely, the nerves of common sensation, or, as it is by 

 some supposed, by nerve-fibres which preside specially over 



