296 



NATURAL HISTORY OF ORGANIZED BODIES. 



pic way some of tlie principal phenomena of the circulation of the blood : 

 1st. The circuit and the continuous current through the whole system of tubes ; 

 with the understanding", however, that the apparatus is intended to represent 

 only one of the two cii'cuits which constitute the circulation in the higlier ani- 

 mals — namely, the greater one. 2d. The formation of two unequal pressures, 

 one rather high, being that of the blood in the arteries ; the other lower, being 

 the venous pressure. 3d. The continuity of the course of the blood in the 

 capillar)^ vessels under the influence of the elasticity of the arteries. 4th. The 

 pulsation which is produced in all the arteries at each systole of the heart. It 

 might be possible to imitate in a more perfect manner the h^-draulic phenomena 

 of tlie course of the blood, but the schema before us suffices for the moment as 

 exhibiting a synthetic reproduction of an action taking place in living beings. 



In studying the circulation, theoretical considerations had led me to conclude 

 tliat the elasticity of the arteries produces on the course of the blood still other 

 effects than those demonstrable by the ajiparatus of Weber, and that this elas- 

 ticit}'^ itself favors the circulation by diminishing tlie obstacle Avhich the heart 

 encounters at each contraction ; in other words, that the heart has less difficulty 

 in emptying itself into elastic vessels than it would meet with if the arterial 

 system were formed of rigid conduits. Now this effect of the arterial elasticity 

 has been contested by tlie Avhole body of physiologists. Some of them have 

 held, with Bichat, that the circulation AVould be effected quite as well in inert 

 tubes as in elastic ones, the only difference being that in inert vessels no pul- 

 sation would be felt. Others, relying on experiment, asserted that two tubes, 

 one elastic, the other inert, give passage to the same quantity of liquid if both 

 have the same calibre ; and this is perfectly true if the flow of the liquid takes 

 place under a constant discharge, but ceases to be true if the afflux of the liquid 

 occurs in an intermittent manner, as is the case with the circulation of the blood. 

 Still other physiologists, struck with the regularity of the course of the blood 

 in the small vessels, have considered the elasticity of the arteries as an additional 

 force, which propels the blood in the arteries during the repose of the heart. 

 But these also were in error, and we might refute their opinion by saying, with 

 Berard, that the elastic force of the arteries is in reality only indirectly contrib- 

 utory, a force cVemprunt^ and that the heart is the sole impulsive agent which 

 exerts an active part in the circulation. Nevertheless, I maintain my proposi- 

 tion : the elasticity of the arteries is favorable to the course of the blood, but 

 it does not act as an impulsive force. It diminishes the resistance wJiich the 

 heart experiences ivhen it projects the hlood in the 'vessels. -The annexed schematic 

 apparatus Avill enable me to demonstrate this proposition. 



A Mariotte vaso V is raised on a support. From this vase proceeds a large 



This tube is bifm-cated at the point T, and 



tube furnished with a faucet R. 



