1891.] Ana'iithetic Action of Pure Nitrogen. 147 



Drs. Bradford and Dean have proved not only the existence of 

 pulmonary vaso-motor nerves, but also that they leave the cord 

 higher up than the systemic vaso-motor nerves (vide ' Roy. Soc. 

 Proc.,' vol. 45). 



These authors remark that " it is probable that the pulmonary 

 vaso-motor mechanism is but poorly developed, compared with that 

 regulating the systemic arteries." 



It would indeed be an incredible physiological anomaly if the 

 vessels of an organ, through which the entire blood of the body has 

 constantly to pass, had not the same regulating and resisting power, 

 compared with the force of the right ventricle, as that possessed by the 

 systemic arterioles. 



Mr. Martin has found by introducing a manometer into a branch of 

 the pulmonary artery of a moderate sized cat, while the remaining 

 branches were suddenly obliterated, that the blood pressure was 

 rather more than doubled, rising from 17 mm. to 36 mm. of mercury. 



Mr. Martin also found that, during the last stages of asphyxia, the 

 pressure in the pnlmonary artery is nearly doubled, while that in the 

 carotid is rapidly falling. 



No experiment that has hitherto been devised can accurately 

 measure the resisting power of the pulmonary arterioles or the actual 

 force of the right ventricle, for the reassn that the arrest or great 

 diminution of the pulmonary circulation weakens the muscular walls 

 of the heart by cutting off the Wood supply through the coronary 

 arteries.* 



The increase of systemic arterial blood pressure, which instantane- 

 ously follows re-admission of air into the lungs, after the circulation 

 had been almost completely arrested by exclusion of air, seems to 

 prove that the heart's walls are not paralysed by venous blood. On 

 the other hand, such a speedy restoration of the circulation is at once 

 explained by the sudden removal of the obstruction which had been 

 caused by the contracted pulmonary arterioles. 



* [Since this paper was communicated to the Royal Society, Dr. M. Foster has 

 done me the favour to refer me to a paper by Professor Knoll (" Der Blutdruck in 

 der Arteria pulmonalis," 'Sitzber. Akad. Wiss. zu Wien,' vol. 97, Abth. 3, p. 207). 

 Dr. Knoll endeavours to measure the normal blood pressure in the pulmonary 

 artery of the rabbit by dividing the sternum, opening the pericardium, and intro- 

 ducing a tube into the pulmonary artery without wounding the pleura. Thus, the 

 blood pressure is observed while normal respiration is carried on. 



Dr. Knoll, however, admits that the atmospheric pressure, consequent on the 

 opening of the mediastinum, cannot be without some influence upon the circulation, 

 o that even this careful and difficult mode of procedure is not free from sources 

 of error. March 3, 1891.] 



