560 THE CRANIAL NERVES. 



complete as to indicate an entire absence of ordinary sensibility. This 

 does not seem to be invariably the case ; but although Bernard has 

 found in some instances a well-marked sensibility in this nerve, and in 

 others only a very indistinct one, it is not possible to say with certainty 

 upon what special conditions the difference depends. As a general 

 rule, the pneumogastric nen'e is decidedly deficient in that kind of sen- 

 sibility which produces pain ; and we know that the organs to which it 

 is distributed have but little appreciation of tactile impressions. Never- 

 theless, there is abundant evidence that this nerve is endowed, in its 

 various divisions, with sensibility of a peculiar kind, and one which is of 

 the highest importance for the due performance of the vital functions. 



Connection with the movements of Respiration. The most important 

 endowment of the pneumogastric nerve is undoubtedly that by which it 

 is connected with the reflex movements of expansion and collapse of 

 the chest in respiration. Its influence in this respect is at once made 

 evident by the results which follow the division of both nerves in their 

 course through the neck. This may be readily done in adult dogs by 

 etherizing the animal and exposing the nerves in the middle of the neck 

 during the continuance of insensibility. After the etherization has 

 passed off, and the circulation and respiration are restored to a quies- 

 cent condition, both nerves may be simultaneously divided, and the 

 effects of the operation observed. 



After the nerves have been divided, and the slight disturbance which 

 immediately follows their section has subsided, the most striking change 

 produced in the condition of the animal is a diminished frequency in 

 the movements of respiration. The respirations sometimes fall at once 

 to ten or fifteen per minute, becoming, in an hour or two, still further 

 reduced. Respiration is performed easily and quietly ; and the animal, 

 if undisturbed, remains usually crouched in a corner, without any spe- 

 cial sign of discomfort. If he be aroused and compelled to move, the 

 frequency of respiration is temporarily augmented ; but as soon as he 

 is again quiet, it returns to its former standard. By the second or 

 third day the respirations are often reduced to five, four, or even three 

 per minute ; when the animal usually appears very sluggish, and is 

 roused with difficulty from his inactive condition. Respiration is also 

 performed in a peculiar manner. The movement of inspiration is slow, 

 easy, and silent, occupying several seconds in its accomplishment; 

 while that of expiration is sudden and audible, and is accompanied by 

 a well marked effort, which has, to some extent, a convulsive character. 

 The intercostal spaces sink inward during the lifting of the ribs ; and 

 the whole movement of respiration has an appearance of insufficiency, 

 as if the lungs were not thoroughly filled with air. This is undoubtedly 

 owing to a peculiar alteration in the pulmonary texture, which has by 

 this time already commenced. 



Death takes place from one to six days after the operation, according 

 to the age and strength of the animal. The only marked symptoms 

 which accompany : * are a steady failure of the respiration, with increas- 



