PNEL'MOGASTKIC NERVE. 471 



therefore, to understand why respiration should be retarded, after 

 section of the pneumogastrics, since the chief source of the stimulus 

 to respiration is cut off; bat the movements still go on. though more 

 slowly than before, because the other sensitive nerves, which con- 

 tinue to act, are also capable, in an imperfect manner, of conveying 

 the same impression. 



The immediate cause of death, after this operation, is no doubt 

 the altered condition of the lungs. These organs are evidently 

 very^ imperfectly filled with air, for some time previous to death ; 

 and their condition, as shown in post-mortem examination, is evi- 

 dently incompatible with a due performance of the respiratory 

 function. It is not at all certain, however, that these alterations 

 in the pulmonary tissue are directly dependent on division of the 

 pneumogastric nerves. It must be recollected that when the sec- 

 tion of the pneumogastrics is performed in the middle of the neck, 

 the filaments of the inferior laryngeal nerves are also divided, and 

 the narrowing of the glottis, produced by their paralysis, must 

 necessarily interfere with the free admission of air into the chest. 

 This difficulty, either alone or combined with the diminished fre- 

 quency of respiration, must have a very considerable effect in im- 

 peding the pulmonary circulation, and bringing the lungs into such 

 a condition as unfits them for maintaining life. 



In order to ascertain the comparative influence upon the lungs 

 of division of the inferior laryngeals and that of the other filaments 

 of the pneumogastrics, we have resorted to the following experi- 

 ment. 



Two pups were taken, belonging to the same litter and of the 

 same size and vigor, about two weeks old. In one of them (No. 1) 

 the pneumogastrics were divided in the middle of the neck ; and 

 in the other (No. 2) a section was made at the same time of the 

 inferior laryngeals, the trunk of the pneumogastrics being left un- 

 touched. For the first few seconds after the operation, there was 

 but little difference in the condition of the two animals. There was 

 the same obstruction of the breath (owing to closure of the glottis), 

 the same gasping and sucking inspiration, and the same frothing at 

 the mouth. Very soon, however, in pup No. 1, the respiratory 

 movements became quiescent, and at the same time much reduced 

 in frequency, falling to ten, eight, and five respirations per minute, 

 as usual after section of the pneumogastrics ; while in No. 2 the 

 respiration continued frequent as well as laborious, and the general 

 signs of agitation and discomfort were kept up for one or two hours. 



