SAPIDITY OF THE ARTERIAL CIRCULATION. 271 



ranged that when the instrument is connected with the artery 

 of a living animal, the current may be instantaneously di- 

 rected through the graduated tube, and by a stop-watch, the 

 length of time occupied in passing from one extremity to 

 the other accurately measured. Observations with this in- 

 strument, on the rapidity of the circulation in the carotid of 

 the dog and -horse, show that the blood moves at the rate of 

 from 10 to 13 inches per second. The rapidity is diminish- 

 ed in the smaller vessels, being but 2*2 inches per second in 

 the metatarsal artery of a horse, and 10 inches in the carotid. 1 



The results thus obtained cannot be received as absolutely 

 exact. The blood is diverted from its natural course, and 

 must experience a certain diminution in velocity from the 

 curves in the tubes. It is also evident that the normal cur- 

 rent is not uniform ; that it is much more rapid immediately 

 after the systole of the heart, than during the diastole ; and, 

 as has been demonstrated by Marey, the blood in the arteries 

 undergoes a certain oscillation. The experiments of Volk- 

 inann give an approximative idea of the mean rapidity, it is 

 true, but they are far from exhibiting the natural current, with 

 the variations corresponding to the movements of the heart. 



A few years later (1858), an instrument was devised by 

 Vierordt, which seemed to embody the right principle, but 

 it was not sufficiently sensitive to accomplish all that was de- 



1 The experiments of Volkmann and Hiittenheim, published in 1846, are re- 

 ferred to, and the instrument described and delineated, in most works on physiol- 

 ogy. When the instrument is first connected with the artery, the blood passes 

 through a straight tube, and is not deviated from its course. The current is 

 diverted into the graduated U tube by two stop-cocks which are arranged so that 

 they may be turned simultaneously. Before it is applied, the apparatus is filled 

 with warm water, so as to prevent the entrance of air into the vessels. 



The following are the results obtained by Volkmann in experiments on dogs 

 and horses : 



In the dog, carotid .... 10'7 inches per second. 



do. do 13 ' " 



In the horse, carotid 10 " " " 



do. metatarsal artery . . 2 '2. " " " 



LONGET, Traite de Physiologic, Paris, 1861, tome i., p. 848. 



