472 THE CRANIAL NERVES. 



The animal, however, after that time became exhausted, cool, and 

 partially insensible, like the other. They both died, between thirty 

 and forty hours after the operation. On post-mortem inspection it 

 was found that the peculiar congestion and solidification of the 

 lungs, considered as characteristic of division of the pneumogastrics, 

 existed to a similar extent in each instance ; and the only appre- 

 ciable difference between the two bodies was that in No. 1 the blood 

 was coagulated, and the abdominal organs natural, while in No. 2 

 the blood was fluid and the abdominal organs congested. We are 

 led, accordingly, to the following conclusions with regard to the 

 effect produced by division of this nerve. 



1. After section of the pneumogastrics, death takes place by a pecu- 

 liar congestion of the lungs. 



2. This congestion is not directly produced by division of the 

 nerves, but is caused by the imperfect admission of air into the 

 chest. 



In adult dogs, the closure of the glottis from paralysis of the 

 laryngeal muscles is less complete than in pups; but it is still 

 sufficient to exert a very decided influence on respiration, and to 

 take an active part in the production of the subsequent morbid 

 phenomena. 



We therefore regard the death which takes place after division 

 of both pneumogastric nerves, as produced in the following man- 

 ner : 



The glottis is first narrowed by paralysis of the laryngeal mus- 

 cles, and an imperfect supply of air is consequently admitted, by 

 each inspiration, into the trachea. Next, the stimulus to respiration 

 being very much diminished, the respiratory movements take place 

 less frequently than usual. From these two causes combined, the 

 blood is imperfectly arterialized. But the usual consequence of 

 such a condition, viz., an increased rapidity of the respiratory 

 movements, does not follow. The imperfect arterialization of 

 the blood does not excite the respiratory muscles to increased 

 activity as it would do in health, owing to the division of the pneu- 

 mogastrics. At the same time, the accumulation of carbonic acid 

 in the blood and in the tissues begins to exert a narcotic effect, 

 diminishing the sensibility of the nervous centres, and tending to 

 retard still more the movements of respiration. Thus all these 

 causes react upon and aggravate each other ; because the connec- 

 tion, naturally existing between imperfectly tirterialized blood and 

 the stimulus to respiration, is now destroyed. The narcotism and 



