114 INFLUENCE OF THE RESPIRATION ON THE HEART. 



The elastic traction of the lungs aids the lesser circulation through the 

 lungs within the chest; the blood of the pulmonary capillaries is 

 exposed to the pressure of the air in the lungs, while the blood in the 

 pulmonary veins is exposed to a less pressure, as the elastic traction of 

 the lungs, by dilating the left auricle favours the outflow from the 

 capillaries into the left auricle. The elastic traction of the lungs acts 

 slightly as a disturbing agent on the right ventricle, and, therefore, 

 on the movement of blood through the pulmonary artery, owing to 

 the overpowering force of the blood-stream through the pulmonary 

 artery, as against the elastic traction of the lungs (Bonders). 



The above apparatus (Fig. 37) shows the effect of the iuspiratory and expiratory 

 movements on the dilatation of the heart, and on the blood-stream in the large 

 blood-vessels. The large glass- vessel represents the thorax; the elastic mem- 

 brane, D, the diaphragm ; P, p, the lungs ; L, the trachea supplied with a stop-cock 

 to represent the glottis ; H, the heart ; E, the vense cavae ; A, the aorta. If the 

 glottis be closed, and the expiratory phase imitated by pushing up D as in I, the 

 air in P, P is compressed, the heart, H, is compressed, the venous valve closes, 

 the arterial is opened, and the fluid is driven out through A. The manometer, 

 M, indicates the intrathoracic pressure. If the glottis be closed, and the 

 inspiratory phase imitated, as in II, p, p and h are dilated, the venous valve 

 opens, the arterial valve closes ; hence, venous blood flows from e into the heart. 

 Thus, inspiration always favours the venous stream, and hinders the arterial ; 

 while expiration hinders the venous, and favours the arterial stream. If the 

 glottis L and I, be open, the air in P, P, /?, p will be changed during the respiratory 

 movements D and d, so that the action on the heart and blood-vessels will be 

 ; diminished, but it will still persist, although to a much less extent. 



