NATURAL HISTORY OF ORGANIZED BODIES. 297 



eacli of its bvanclics is continued by a long conduit. One b h' is elastic, being 

 fonned of thin caoutcliouc ; the other a a' is of glass, and consequently rigid. 

 A valve, placed at the origin of the clastic tube, permits the liquid to penetrate 

 freely into its interior, but opposes all reflux in an inverse direction. The two 

 tubes have the same capacity of discharge: of this we may convince ourselves 

 by ojjening the faucet 11 and allowing a continuous current to be established. 

 But if the faucet be opened and closed alternately, it will be seen that the efflux 

 by the inert tube is intermittent, while that by the elastic tube is continuous ; 

 it will be also found that the discharge has become very imequal, and that much 

 less of the liquid escapes by the inert than by the elastic tid)e. The proposition 

 might be considered, then, as already proved, for it is evident that if the elastic 

 tube has discharged more liquid than the other, this results from its having 

 received more, and as the penetration of the liquid into the tubes takes place 

 under a constant charge, and can only be effected at the time when the faucet is 

 open, this clearly proves that at those instants the tube of glass was more per- 

 meable than the elastic tube. 



But we may form a more exact conception of what occurs under these condi- 

 tions by inquiring not what issues from the tubes, l)ut what enters them. The 

 Mariotte vase employed as a source of supply furnishes the means of knowing 

 accurately what penetrates into each of the tubes at a given moment, for not the 

 smallest quantity of liquid can issue from the vase without the indication of what 

 portion of it is withdrawn by the entrance of a more or less considerable quantity 

 of air. Now, if the liquid be permitted to flow l)y the elastic tube alone, or the 

 glass tube alone, it will be seen that in the two cases the Slariotte vase indicates 

 very different discharges. If the efflux be by the ine^'t tube alone, bubbles of 

 air are seen to enter the vase one by one, at regular intervals, until the sup- 

 pression of the flow of liquid, when, by the same act, the entrance of the bubbles 

 is aiTcsted. If, on the other hand, the inert tube being closed, the efflux 

 commences with the elastic tube alone, a mass of air is seen on the instant to 

 rush into the vase, announcing the escape of a wave of the liquid at the first 

 moment ; the bubbles then become more rare and enter with the same slowness 

 which was observed in the case of efflux by the inert tube. Let the faucet be 

 closed at this instant, and it will plainly aj)pear that the elastic tube has 

 received a quantit}^ of liquid greater than that received by the inert tube and 

 corresponding to the access of the large volume of air at the commencement 

 of the experiment. It is this excess of liquid which occasions a flow more or 

 less durable alter the closing of the faucet. This whole quantity of water accom- 

 modated by the distension of the tube constitutes the advantage of the elastic 

 tube as regards thfe afflux. If this tube more readily admits the penetration 

 of the water into its interior, it is because the liquid is not required, as in the 

 case of the inert tulie, to overcome the total friction and flow outwardly, but 

 finds lodgment within the tube by reason of the extensibilit}- of the latter. It 

 is obvious that as often as these intermittent openings of the faucet are repeated 

 a new advantage is created in favor of the elastic tube. Finally, theory teaches 

 us that to render the efflux by the two tubes as unequal as possible, it is 

 requisite that the faucet should be opened, each time for a very brief period, and 

 that the intervals between the openings should be of some duration. 



The demonstration of this effect of the elasticity of the arteries, though here- 

 tofore unknown, would seem to be of much importance ; it has enabled uie to 

 draw new conclusions, and to establish, for example, that if the arteries lose their 

 elasticity, as is normally the case with aged persons, the heart must experience 

 an increase of resistance, and, according to the known laws of pathology, become 

 hypertrophied. The researches which I have made with a view to the verifica- 

 tion of tins prevision have fin-nished a complete confirmation of the tlieory, but 

 I shall not insist here on particulars which enter properly into the domain of 

 medicine, and which would divert me from my subject. 



