INFLUENCE OF NERYOUS SYSTEM. 393 



as in the muscles and other tissues of a paralysed face or 

 limb, it may appear as if the atrophy were the direct con- 

 sequence 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 nutri- 

 tion will be less defective (J. Eeid). The defect of the 

 nutritive process which ensues in the face and other parts, 

 in consequence of destruction of the trigeminal nerve, 

 must be referred directly or indirectly to the loss of 

 influence exercised through the sensitive or sympathetic 

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

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

 nutrition 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. 



The influence exercised by the sensitive and sympathetic 

 nerves over the process of nutrition, thus proved in the 

 case of the trigeminal nerve, is probably only an example 

 of what is generally true. A similar influence is shown 

 in the cases in which sloughing of parts from injury or 

 disease of the spinal cord has ensued earlier and more 

 extensively when sensation than when motion alone was 

 lost, and in other cases in which the wasting of a paralysed 

 limb is, after a certain time, more marked when both 

 sensation and motion are impaired than when the power 

 of motion alone is interfered with. 



It is not at present possible to say whether the influence 

 on nutrition is exercised through the sensitive or through 

 the sympathetic nerves, which, in the parts on which the 

 observation has been made, are generally combined in the 

 same sheath. The truth perhaps is, that it may be exerted 

 through either or both of these nerves. The defect of 

 nutrition which ensues after lesion of the spinal cord 

 alone, the sympathetic nerves being uninjured, and the 



