ELASTICITY OF THE AKTERIES. 249 



The elasticity of tlie arteries favors the flow of the blood 

 toward the capillaries bj a mechanism which is easily un- 

 derstood. The blood discharged from the heart distends the 

 elastic vessel, which reacts, after the distending force ceases 

 to operate, and compresses its fluid contents. This reaction 

 would have a tendency to force the blood in two directions, 

 were it not for an instantaneous closure of the valves, which 

 makes regurgitation impossible. The influence then can only 

 be exerted in the direction of the periphery ; and, if we can 

 imagine as divided an action which is propagated with such 

 rapidity, the reaction of that portion of the vessel immedi- 

 ately distended by the heart, distends a portion farther on, 

 which in its turn distends another portion, and so the wave 

 passes along until the blood is discharged into the capillaries. 

 In this way we can see that in vessels removed a sufficient 

 distance from the heart, the force exerted on the blood by 

 the reaction of the elastic walls is competent to produce a 

 very considerable current during the intervals of the heart's 

 contraction. 



This theoretical view is fully carried out by the following 

 simple and conclusive experiment of M. Marey. He con- 

 nected two tubes of equal size, one of rubber and the other 

 of glass, with the stop-cock of a large vase filled with water. 

 The elastic tube was provided with a valve near the stop- 

 cock, which prevented the reflux of fluid, and both were 

 fitted with tips of equal caliber. When, by alternately opening 

 and closing the stop-cock, water was allowed to flow into these 

 tubes in an intermittent stream, it was found that a greater 

 quantity was discharged by the elastic tube ; but an equal 

 quantity was discharged by both tubes when the stop-cock 

 was left open, and the fluid allowed to pass in a continuous 

 stream. 1 



This simple experiment shows that not only does the elas- 

 ticity of the arteries convert the intermittent current in the 

 largest vessels into a current more and more nearly contin- 



1 MAREY, Circulation du Sang, Paris, 1863, pp. 128, 131. 



