218 CIRCULATION. 



If the organ be exposed in a living animal, and a canula be 

 introduced through the walls into one of the ventricles, we 

 have a powerful jet at each systole, but no blood is discharged 

 during the diastole. The same absolute intermittency of the 

 current will be seen if the aorta be divided. It is evident 

 that we must look to the arteries themselves for the force 

 which produces a flow of blood in the intervals of the heart's 

 action. The conversion of the intermittent current in the 

 largest vessels into a nearly constant flow in the smallest 

 arterioles is effected by the physical property of elas- 

 ticity. This may be illustrated in any elastic tube of 

 sufficient length. If we connect with a syringe a series of 

 rubber tubes progressively diminishing in caliber, and dis- 

 charging by a very small orifice, and inject water in an in- 

 termittent current, if the apparatus be properly adjusted, 

 the fluid will be discharged at the end of the tube in a 

 continuous stream. Nearer the syringe, the stream will 

 be remittent ; and directly at the point of connection of 

 the syringe with the tube, the stream will be intermittent. 

 The intermittent impulse may be said, in this case, to be 

 progressively absorbed by the elastic walls of the tube. Each 

 impulse first distends that portion of the tube nearest to it, 

 and further on, the distention is diminished, until it becomes 

 inappreciable. If the syringe be connected with two tubes, 

 one elastic and the other inelastic, the current will be either 

 remittent or continuous in the one, and intermittent in the 

 other. 



This modification of the impulse of the heart has great 

 physiological importance; for it is evidently essential that 

 the current of blood, as it flows into the delicate capillary 

 vessels, should not be alternately intermitted, and impelled 

 with the full power of the ventricle. After all, it is in the 

 capillaries that the blood performs its functions, and here we 

 should have a constant supply of the fluid in proper quantity 

 and in proper condition to meet the nutritive requirements 

 of the parts. 



