BY DR. BURDON-S ANDERSON. 335 



artery into a recipient for the analysis of its gases, at from half 

 a minute to a minute after the beginning of the inhalation of 

 nitrogen, the animal being already in the second stage of as- 

 phyxia. It was found, for example, 1 that the blood of an animal 

 which before breathing nitrogen contained 18.8 per cent, per 

 vol. of oxygen (at 760 millim. and C.), contained after breath- 

 ing nitrogen for one minute a mere trace of oxygen (0.3 per 

 cent.) ; during the same period the carbonic acid gas had dimin- 

 ished from 47.2 per cent, to 39.4 per cent. These experiments 

 are referred to here on account of their fundamental importance. 

 They are much too difficult for repetition. 



114. Demonstration that the Pulmonary Termina- 

 tions of the Vagus Nerves are Excited by Distension 

 of the Lungs. It was long ago surmised by physiologists 

 (particularly by Rosenthal) that the pulmonary branches of 

 the vagus nerves contain afferent fibres, which are excited by 

 the expansion of that organ, and that these fibres take part in 

 the regulation both of the movements of the heart and those of 

 respiration. The proof of this has been lately given by Hering. 

 A dog having been narcotized with morphia or opium, one arm 

 of a T-shaped canula is secured in the trachea, the other being 

 connected with a mercurial manometer. To the stem an India- 

 rubber connector is fitted, which is guarded by a screw clip, 

 and ends in a blowing tube: a canula is placed in the carotid 

 and connected with the kymograph. These preparations having 

 been made, an observation of arterial pressure is taken. The 

 clockwork being still in motion, the experimenter distends the 

 lungs of the animal until the distal column of the manometer 

 stands about 30 or 40 millimetres above the other, and then 

 closes the clip. Two important results are produced. In the 

 first place, the inspiratory muscles are thrown out of action, 

 and remain relaxed so long as the distension lasts, while those 

 of expiration are brought into continuous and energetic con- 

 traction ; and secondly, the frequency of the contractions of 

 the heart is more than doubled. In the preceding experiment 

 the circulation is considerably affected by the increased pres- 

 sure exercised by the distended lungs on the heart and great 

 veins ; consequently, the increased frequency of the pulse might 

 be attributed in whole or in part to this circumstance rather 

 than to the pulmonary distension. To meet this objection, the 

 experiment may be modified as follows : A dog is narcotized 

 and respiration maintained artificially, the apparatus being so 

 arranged that at any moment the lungs may be dist\nded as 

 in the last case. This done, the thoracic organs are completely 

 exposed by removing the anterior wall of the chest in the man- 

 ner described in 49 : it is then seen that the effect of inflation 



1 Pfliiger's Archiv., vol. I p. 94. 



