Chap, xm.] CIRCULATION. 221 



trunks called vence cavoe. Of these two trunks the higher one 

 receives the venous blood of the higher part of the body ; the 

 other is the general trunk of the veins of the lower half. Both 

 throw themselves into the right auricle of the heart, whence 

 the venous sanguineous wave passes into the corresponding ven- 

 tricle, which drives it in its turn into the lungs, where it is oxy- 

 genised, arterialised, to return into the right auricle, to pass into 

 the ventricle of the same side, and recommence the cycle. 



The impulsion of the heart, not very perceptible in the 

 capillaries, where the blood moves in an unintermitting flow, 

 seems to be almost null in the veins. There the causes of the 

 circulation are especially the reflux of the liquids exhaled by the 

 anatomical elements, and principally the elasticity and the 

 contractility of the venous canals, in most of which, besides, 

 all retrogradation of the sanguineous current is rendered im- 

 possible by valves arranged in such, a manner that they leave 

 the path free in the direction of the heart, but can shut it in the 

 direction of the capillaries. 



The grand system of sanguineous irrigation which we have 

 just described functionates consequently without repose, without 

 pause, as long as life endures. Unceasingly a stream of 

 nourishing blood traverses it. This stream wastes its strength 

 in the tissues, regains its strength at the expense of the sub- 

 stances elaborated by the digestive apparatus, renews its vivifying 

 gas in the respiratory capillaries, exhausts itself in the capillaries 

 of the glands. It is literally a living river. But by the side of 

 the grand sanguineous system exists another network with which 

 we have now to occupy ourselves. 



