320 CIRCULATION. 



blood flowed from the extremity of the sound only in the 

 moment of expiration. We obtain results entirely analogous 

 if we introduce the sound into the crural vein, directing it 

 toward the abdomen." l As several contractions of the right 

 auricle occur between two acts of respiration, it is shown by 

 this experiment that, during inspiration, the suction force is 

 sufficient to counterbalance the contractions of the auricle, 

 which would otherwise force a certain quantity of blood 

 through the sound, as it does during expiration ; for then we 

 have a jet synchronous with the beats of the heart. Cathe- 

 terization of the right side of the heart is now quite a common 

 experiment ; and we have frequently observed the variations 

 in the flow of blood from a sound introduced through the 

 jugular, which were mentioned by Magendie. The suction 

 force is still more strikingly exhibited in this operation by 

 the entrance of air, which is frequently drawn into the heart 

 during a violent inspiration. 



The influence of aspiration on the circulation in the veins 

 was still more minutely studied in 1825 by Barry, whose 

 most important experiments have been repeated, with some 

 modifications, by Poiseuille. Barry introduced through the 

 jugular of a horse a bent tube of glass, one extremity being 

 passed into the right cavities of the heart, or the vena cava, 

 and the other into a vessel containing a colored liquid. He 

 found that with each act of inspiration the liquid mounted 

 up in the tube, demonstrating the operation of a notable suc- 

 tion force. The observations and experiments of Barry were 

 made on quite an extended scale, but many of his conclusions 

 were not entirely warranted. He studied, for example, the 

 effect of preventing the entrance of air into the chest by the 

 trachea, and found that this increased the suction force very 

 considerably, as indicated by the greater elevation of liquid 

 in the tube with each inspiratory effort ; but he supposed 



1 MAGENDIE, Influences des Mouvements de la Poitrine el des Efforts sur la Cir- 

 culation du Sang. Journal de Physiologic Experimentale, Paris, 1821, tome i., 

 p. 136. 



