176 NERVOUS SYSTEM. 



tendency to draw the lips of the glottis together, while they 

 assist in passing the alimentary bolus into the oesophagus. 

 When these important acts are wanting, there is some diffi- 

 culty in the process of deglutition itself as well as danger of 

 the passage of alimentary particles into the larynx. 



Influence of the Spinal Accessory upon the Heart. 

 When we come to study the varied functions of the pneumo- 

 gastrics, we will discuss fully the mechanism by which the 

 contractions of the heart are arrested by galvanization of both 

 of these nerves in the neck. A very curious and interesting 

 observation by Waller has demonstrated that this influence, 

 whatever be its mechanism, is derived from the spinal acces- 

 sory, and necessarily comes through its communicating 

 branch. It has been found that a powerful current of gal- 

 vanism passed through the pneumogastric on one side will 

 arrest the action of the heart. Waller found that if he ex- 

 tirpated the spinal accessory on one side, the action of the 

 heart could not be arrested by galvanizing the pneumo- 

 gastric upon the same side ; but this result followed gal- 

 vanization of the pneumogastric upon the opposite side, on 

 which the connections with the spinal accessory were intact. 

 These phenomena, however, could not be observed until 

 from ten to twelve days had elapsed after the extirpation of 

 the spinal accessory. 1 We have already seen, in treating of 

 the general properties of the nerves, that the irritability of 

 the motor nerves disappears in about four days after their 

 separation from the nerve-centres. 2 In the observation just 

 referred to, it seemed necessary that a sufficient time should 

 elapse after extirpation of the spinal accessory for the irrita- 



1 WALLER, Experiences sur les nerfs pneumogastriques et accessoires de Willis. 

 Gazette medicate, Paris, 1856, 3eme serie, tome xi., p. 420. 



In these experiments, Waller demonstrated by microscopical examination 

 the disorganization of both "branches of the spinal accessory, and showed that 

 their galvanization produced little, if any contraction in the muscles to which 

 these branches were distributed. 



3 See p. 96u 



