THE CIRCULATION OF THE BLOOD AND LYMPH 115 



second in the carotid of the rabbit, and from over 500 mm. 

 to less than 250 mm. in the carotid of the dog. Chauveau, 

 with the dromograph, found the velocity in the carotid of a 

 horse to be 520 mm. per second during systole, 150 mm. 

 during diastole, 220 mm. during the period of the dicrotic 

 wave. 



It is probable, however, that if these numbers are at all 

 accurate for bloodvessels in the immediate neighbourhood 

 of the heart, there must be a rapid diminution in the 

 velocity even while the arteries are still of considerable 

 calibre. For it has been found by the electrical method 

 that, in anaesthetized dogs at any rate, as is shown in the 

 following table, the mean velocity between the origin of the 

 aorta and the crural artery in the middle of the thigh is 

 usually less than 100 mm. per second. 



In I. the injecting cannula was in the descending part of the 

 thoracic aorta, in V. at the very origin of the aorta, and in II., III. 

 and IV. in the left ventricle. 



As to the speed of the blood in the arteries of man, our 

 data are insufficient for more than a loose estimate. But it 

 does not seem likely that the mean velocity of a particle of 

 blood in moving from the heart to the femoral artery can 

 exceed 150 mm. per second for the whole of its path. This 

 would correspond to rather more than a third of a mile per 

 hour. In the arch of the aorta the average speed may be 

 twice as great. ' The rivers of the blood ' are, even at their 

 fastest, no more rapid than a sluggish stream. A red 

 corpuscle, even if it continued to move with the velocity 

 with which it set out through the aorta, would only cover 



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