436 PHYSIOLOGY CHAP. 



XIII. It is easy from the above to deduce the beneficial influ- 

 ence of the respiratory mechanism upon the circulation of the blood 

 (and lymph), as shown more particularly in the aspiration exerted 

 by the thorax during inspiration, which accelerates the centripetal 

 current, and increases the filling of the heart. This inspiratory 

 influence cannot be eliminated by the contrary effects of the 

 expiratory movements, particularly when the abdominal muscles 

 intervene actively, as has constantly been verified on certain 

 animals. 



Some observers, however, particularly Filippo Pacini in Italy, 

 have exaggerated the importance of the respiratory mechanism on 

 the circulation of the blood, contending that a drowned person 

 whose cardiac movements have practically ceased, can be brought 

 back to life merely by artificial respiration. The untenability of 

 this view is shown by two classical experiments, one devised by 

 Valsalva (1740), the other by Johannes Miiller (1838), which 

 consist in determining what influence can be exerted by the 

 respiratory movements on the circulation, under conditions in 

 which the respiratory oscillations of intrathoracic and intra- 

 abdominal pressure are in a position to exert maximal influence 

 upon the course of the blood, or more accurately upon the entrance 

 and exit of the blood from the thoracic cavity. 



If the glottis is closed after a deep inspiration, and a strenuous 

 and prolonged expiratory effort is then made, such pressure can be 

 exerted on the heart and intrathoracic vessels that the movements 

 and flow of the blood are temporarily arrested (Valsalva). Pro- 

 nounced swelling of the veins, visible principally in those of the 

 neck and face, evacuation of the vessels in the pulmonary system, 

 and surcharge of the systemic circulation, cessation of cardiac 

 sounds, and disappearance of the arterial pulse, can all be witnessed 

 (E. H. Weber, Bonders). 



If instead of a forced expiration, the glottis is closed, and a 

 prolonged inspiratory movement made, the heart and all the intra- 

 thoracic vessels fill to such an extent that the arterial pulsations 

 cease, owing to the surcharge of the lesser, and comparative 

 evacuation of the greater circulation (J. Miiller). 



These experiments cannot be performed without a certain 

 amount of risk, particularly to individuals who are no longer 

 young, and whose cardio- vascular system is no longer vigorous and 

 functioning normally. They may, however, be conveniently re- 

 produced on an artificial schema which represents the thoracic 

 cavity, lungs, heart, and related vessels, as shown in Fig. 201. 



The results of these researches show that the respiratory 

 movements are only favourable to the circulation of the blood 

 when they are performed quietly, in a normal manner and with open 

 glottis, so as not to disturb cardiac activity, or compress or dilate 

 the heart to any extent. It is then seen (as can readily be con- 



