238 NERVOUS SYSTEM. 



An artery was then exposed and the color of the blood 

 noted. "When the artificial respiration was arrested, the 

 animal made efforts to breathe as soon as the blood became 

 dark in the arterial system. "We concluded from this, that 

 the impression conveyed to the respiratory nervous centre, 

 giving rise to the movements of respiration, was due to the 

 action of the non-oxygenated blood. 



To ascertain whether the impression were made upon 

 the nerves distributed to the lungs or upon other nerves, 

 a large vessel was divided and the system was drained of 

 blood, the lungs being continually supplied with fresh air. 

 In this case, respiratory efforts of the most- violent character 

 were invariably noted following the haemorrhage. This por- 

 tion of the experiment demonstrated that the sense of want 

 of air was not dependent upon the accumulation of carbonic 

 acid in the lungs, but was due to a deficient supply of the 

 oxygen-carrying fluid to the general system. It further 

 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 modifica- 

 tion, 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, though they are curious and inter- 

 esting, do not throw much light upon the relations of these 



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, October, 1861. Since this publication, the experiments have been 

 frequently repeated in public demonstrations, and the conclusions verified. 



