6io A MANUAL OF PHYSIOLOGY 



tion. When the muscle is curarized and the nerves thus 

 eliminated the excitability to induced currents is found to 

 be diminished. The same is the case in a muscle which 

 exhibits the reaction of degeneration after section of its 

 motor nerve, only the loss of excitability to induced currents 

 is greater, and may even be complete. The closing anodic 

 contraction is stronger than the closing kathodic the 

 opposite of the ordinary law. The nerves are inexcitable 

 either to constant or induced currents. The reaction of 

 degeneration is only obtained from paralyzed muscles when 

 the paralyzing lesion is situated in the cells of the anterior 

 horn from which the motor nerves take origin, or below that 

 level. Accordingly, it is sometimes of use in localizing the 

 position of a lesion. For instance, a group of muscles might 

 be paralyzed by a lesion in the grey matter of the brain or 

 in the nerve-fibres connecting this with the grey matter of 

 the anterior horn of the cord, or in the grey matter of the 

 anterior horn itself, or in the peripheral nerve-fibres leading 

 from this to the muscles. In the first two cases the reaction 

 of degeneration would be absent, although the muscles, if 

 the lesion was of long standing, would be atrophied to some 

 extent ; in the last two there would be acute atrophy of the 

 muscles and the reaction of degeneration would be obtained. 



Trophic Nerves. The fact that the proper nutrition of 

 nerve-fibres is dependent on their connection with nerve- 

 cells has been by some writers generalized into the doctrine 

 that all tissues are provided with * trophic ' nerves, which, 

 apart from any influence on functional activity, regulate 

 the nutrition of the organs they supply. But the evidence 

 for this view, when weighed in the balance, is found want- 

 ing ; and it may be said that up to the present no unequivocal 

 proof } experimental or clinical, has ever been given of the existence 

 of specific trophic nerves. 



It is true that division of the trigeminus nerve within the 

 skull is sometimes followed by cloudiness of the cornea, 

 going on to ulceration, and ultimately inflammation and 

 destruction of the eyeball. Ulcers also form on the lips and 

 on the mucous membrane of the mouth and gums ; and the 

 nasal mucous membrane on the side corresponding to the 



