ELASTICITY OF THE AKTEEIE8. 247 



charge of blood which enters at each pulsation, renders the 

 actual distention of the vessels less than we should be led to 

 expect from the force of the heart's contraction. The most 

 satisfactory experiments on this subject are those of Poiseu- 

 ille. 1 This observer illustrated the dilatation of the arteries 

 in the following way : Having exposed a considerable extent 

 of the primitive carotid in a horse, he enclosed a portion in a 

 tin tube filled with water and connected with a small upright 

 graduated tube of glass. The openings around the artery, as 

 it passed in and out of the apparatus, being carefully sealed 

 with tallow, it is evident that any dilatation of the vessel 

 would be indicated by an elevation of the water in the grad- 

 uated tube. This experiment invariably showed a marked 

 dilatation of the artery with each contraction of the heart. 



" We remark that the dilatation is not very considerable ; 

 thus it is not easy to recognize it by simple inspection, in an 

 artery of even the caliber of that which occupies us, after we 

 have it exposed." 2 



It being fully established that the arteries are dilated with 

 each ventricular systole, it becomes important to study the 

 influence of their elasticity upon the current of blood. Divi- 

 sion of an artery in a living animal exhibits one of the im- 

 portant phenomena due to the elastic and yielding character 

 of its walls. We observe, even in vessels of considerable 

 size, as the carotid or femoral, that the flow of blood is not 

 intermittent, but remittent. With each ventricular systole 

 there is a sudden and marked impulse ; but during the inter- 

 vals of contraction, the blood continues to flow with consid- 

 erable force. As we recede from the heart, the impulse 

 becomes less and less marked ; but it is not entirely lost, even 

 in the smallest vessels, the flow becoming constant only in 

 the capillary system. That the force of the heart is abso- 

 lutely intermittent, is shown by the following experiment : 



1 POISEUILLE, Recherchcs sur V Action des Arteres dans la Circulation, Arie- 

 rielle, Journal de la Physiologic, 1829, tome ix., p. 44. 

 3 Ibid., p. 48. 



