RESPIRATION. 



201 



within the right auricle itself, will draw the blood into the thorax, and 

 so assist the circulation. This suction action is independent of the suc- 

 tion power of the diastole of the auricle about which we have previously 

 spoken (p. 127). The effect of sucking more blood into the right auricle 

 will, cceteris paribus, increase the amount passing through the right 

 ventricle, which also exerts a similar suction action, and through the 

 lungs into the left auricle and ventricle and thus into the aorta. This 

 all tends to increase the arterial tension. The effect of the diminished 

 pressure upon the pulmonary vessels will also help towards the same 

 end, i. e.. an increased flow through the lungs, so that, as far as the 



FIG. 161. Diagram of an apparatus illustrating the effect of inspiration upon the heart and 



, , 



and A, the aorta; nZ, -LI, the right and left lung; T, the trachea; M, mercurial manometer in connec- 

 tion with the pleura. The increase in the capacity of the box representing the thorax is seen to 

 dilate the heart as well as the lungs, and so to pump in blood through v, whereas the valve prevents 

 reflex through A. The position of the mercury in M shows also the suction which is taking place. 



heart and its veins are concerned, inspiration increases the blood pres- 

 sure in the arteries. The effect of inspiration upon the aorta and its 

 branches within the thorax would be, however, contrary; for as the pres- 

 sure outside is diminished the vessels would tend to expand, and thus to 

 diminish the tension of the blood within them, but inasmuch as the large 

 arteries are capable of little expansion beyond their natural calibre, the 

 diminution of the arterial tension caused by this means would be insuf- 



