214: NERVOUS SYSTEM. 



The first of these conditions is easily fulfilled. All that 

 is necessary is to stimulate the roots before the nerves have 

 received any anastomosing filaments. To avoid contractions 

 of muscles due to reflex action, it is best to divide the roots 

 and to stimulate their distal portion. If it be true that 

 stimulation of the distal extremities of the roots, the irrita- 

 tion so applied as not to involve communicating filaments 

 from motor nerves, and not to be conveyed to the centres, 

 producing reflex movements through other nerves, does not 

 produce any movements, it is fair to assume that the true 

 filaments of origin are exclusively sensory. The facts upon 

 this point demand careful and critical study ; and it will be 

 proper to discard the earlier experiments, made before the 

 mechanism of reflex action had been satisfactorily estab- 

 lished. 



If the experiments of Longet be accepted without re- 

 serve, they prove as conclusively as is possible without ex- 

 posing the roots in living animals, an operation which is 

 impracticable that the true filaments of origin of the pneu- 

 mogastrics are exclusively sensory; at least, that the nerve 

 contains no motor filaments except those derived from other 

 nerves. The following quotation gives the essential points 

 in these experiments : 



" In dogs of large size and in horses, I have isolated in 

 the cranium, with the most minute care, the pneumogastric 

 of the medulla oblongata and the superior filaments of the 

 spinal accessory (internal ~branch\ in order to avoid all reflex 

 movement and any derivative current upon the last-named 

 nerve ; I then immediately caused the current to act exclu 

 sively upon the filaments of origin of the pneumogastric, 

 without having ever seen the slightest contraction super- 

 vene, either in the muscles of the larynx or pharynx, or in 

 the muscular tunic of the oesophagus, or elsewhere. 



" But also I have never failed to demonstrate to all those 

 who witnessed my experiments, how it is easy to obtain op- 

 posite results in neglecting only one precaution : it suffices, 



