582 NERVOUS SYSTEM. 



experiments upon which the explanation offered by Bernard is based, it is 

 sufficient to state that he observed a traumatic emphysema as a consequence 

 of the excessively labored and profound inspirations. Indeed, this can be actu- 

 ally seen when the pleura is exposed in living animals. As a result of this 

 excessive distention of the air-cells, the pulmonary capillaries are ruptured in 

 different parts, the blood becomes coagulated and the lungs are finally solidi- 

 fied. This can not occur in birds, because the lungs are fixed, and their rela- 

 tions are such that they are not exposed to excessive distention in inspiration. 



The pneumogastrics sometimes reunite after division. The following 

 observation (Flint, 1874) illustrates this fact, which has frequently been 

 noted : Both pneumogastrics were divided in the neck in a medium-sized 

 dog. The pulse was immediately increased from one hundred and twenty 

 to two hundred and forty in the minute, and the number of respirations fell 

 from twenty-four to four or six. In ten days the pulse and respirations had 

 become normal. The dog was then killed by section of the medulla oblon- 

 gata, and the reunion of the divided ends of the nerves was found to be 

 nearly complete. 



The relations of the pneumogastrics to the respiratory nervous centre 

 have been fully considered in connection with the physiology of respiration. 



Effects of Faradization of the Pneumogastrics upon Respiration. Fara- 

 dization of the pneumogastrics in the neck, if the current be sufficiently 

 powerful, arrests respiration. This arrest may be produced at any time with 

 reference to the respiratory act, either in expiration or inspiration, although 

 it is more readily effected in expiration. During the passage of the current 

 the general movements of the animal are also arrested. Although respira- 

 tion may always be arrested in this way, quite a powerful current is required. 

 During the passage of a very feeble current, the respirations are accelerated. 

 They are then retarded as the current is made stronger, until they finally 

 cease (Bert). 



The following are the phenomena, observed by Bert, during the passage 

 of a powerful Faradic current : 



" If an excitation be employed sufficiently powerful to arrest respiration 

 in inspiration, all respiratory movements may be made to cease at the very 

 moment when the excitation is applied (inspiration, half-inspiration, expira- 

 tion), either by operating upon the pneumogastric, or operating upon the 

 laryngeal. . . . 



" Any feeble excitation of centripetal nerves increases the number of the 

 respiratory movements ; any powerful excitation diminishes them. A pow- 

 erful excitation of the pneumogastrics, of the superior laryngeal, of the nasal 

 branch of the infraorbital, may arrest them completely ; if the excitation be 

 sufficiently energetic, the arrest takes place at the very moment it is applied. 

 Finally, sudden death of the animal may follow a too powerful impression 

 thus transmitted to the respiratory centre : all this being true for certain 

 mammalia, birds and reptiles." 



The above expresses the most important experimental facts at present 

 known with regard to the influence of stimulation of the pneumogastrics 



