PNEUMOGASTRIC, OR PAR VAGUM NERVE. 661 



supply of the oxygen-carrying fluid to the general system. It farther demonstrated that 

 the impression in the general system was not due to the presence of carbonic acid 

 but to the absence of oxygen ; for no blood containing carbonic acid circulated in the 

 system. 



These phenomena were observed without any modification, after division of both 

 pneumogastric nerves in the neck, and they seem to prove conclusively that the sense of 

 want of air is not transmitted to the respiratory nervous centre through the medium of 

 these nerves. 1 



Effects of Galvanization of the Pneumogastrics upon Respiration. The phenomena 

 which follow galvanization of the pneumogastrics, although they are curious and inter- 

 esting, do not throw much light upon the relations of these nerves to respiration. We 

 have already mentioned the arrest of the respiratory movements by galvanization of the 

 superior laryngeal branches and of the central ends of the pneumogastrics after their divi- 

 sion in the neck. The main point of interest in this connection is the fact that the effects 

 observed are entirely reflex, galvanization of the peripheral ends of the divided nerves 

 having no direct action on the movements of the thorax. 



In view of the very indefinite physiological applications of the experiments made by 

 galvanizing the nerves, we shall not give in detail the numerous observations upon this 

 subject, but shall simply state the results, as given in a recent and very elaborate work 

 upon respiration, by M. Bert : 



" 1. Respiration may be arrested by excitation of the pneumogastrics (Traube), of the 

 larynx (Cl. Bernard), of the nostrils (M. Schiff), of most of the sensory nerves (M. Schiff, 

 an assertion that I have not been able to verify). 



" 2. This arrest may take place either in inspiration or in expiration, through any one 

 of these nerves, without attributing it to the action of derived currents. 



" 3. A feeble excitation accelerates the respiration ; a more powerful excitation 

 retards it ; a very powerful excitation arrests it. These words ' feeble ' and ' powerful ' 

 having, it is understood, only a relative sense for any one animal and under certain con- 

 ditions : what is feeble for one would be powerful for another, etc. 



" I believe, in opposition to the opinion of Rosenthal, that section of the pneumogas- 

 trics does not increase the difficulty of arresting respiration ; at least, death by excitation 

 occurs much more easily in this case. 



" 4. When the respiratory movements are completely arrested, it is always the same 

 for the general movements of the animal, which remains motionless. 



" 5. Respiration returns even during excitation, and when this is arrested, it almost 

 always becomes accelerated. 



"6. Arrest in expiration is more easily obtained than arrest in inspiration ; there are 

 animals, indeed, in which it is impossible to effect the latter. 



"7. If an excitation be employed sufficiently powerful to arrest respiration in inspi- 

 ration, all respiratory movements may be made to cease at the very moment when the 

 excitation is applied (inspiration, half-inspiration, expiration), 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 powerful excitation of the 

 pneumogastrics, of the superior laryngeal, of the nasal branch of the infra- orbital, 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 r all this being true for 

 certain mammalia, birds, and reptiles." 



1 For a full account of these experiments, with their bearing upon certain respiratory phenomena before birth, the 

 reader is referred to the original article, entitled Experimental Researches on Points connected with the Action of 

 the Heart and with Respiration, published in the American Journal of the Medical Sciences, Philadelphia, Octo- 

 ber, 1861. Since this publication, the experiments have been frequently repeated in public demonstrations, and the 

 conclusions verified. 



