178 THE MOTION OF THE BLOOD. 



" Weiss 2 , and after him Sabatier a , ascribe to this cause like- 

 wise the comparatively larger size b of the right auricle and ven- 

 tricle after death, especially in the adult subject. 



" The motion of the blood is performed by these two orders 

 of vessels in conjunction with the heart. Its celerity in health 

 cannot be determined ; for this varies not only in different per- 

 sons, but in different parts of the same person. 



" Generally, the blood moves more slowly in the veins than 

 in the arteries, and in the small vessels than in the large trunks, 

 although these differences have been overrated by physiologists. 



" The mean velocity of the blood flowing into the aorta is 

 usually estimated at eight inches for each pulsation, or about fifty 

 feet in a minute. 



" Some have affirmed that the globules of the cruor move more 

 in the axes of the vessels, and with greater rapidity, than the 

 other constituents of the blood. I know not whether this rests 

 upon any satisfactory experiment, or upon an improper applica- 

 tion of the laws of hydraulics ; improper, because it is absurd to 

 refer the motion of the blood through living canals to the mere 

 mechanical laws of water moving in an hydraulic machine. I 

 have never been able to observe this peculiarity of the globules. 



" My persuasion is still more certain that the globules pass on 

 with the other constituents of the blood, and are not rotated 

 around their own axis; that besides the progressive, there is no 

 intestine motion in the blood, although indeed there can be no 

 doubt that the elements of this fluid are occasionally divided, 

 where they are variously impelled, according to the different di- 

 rection, division, and anastomoses of the vessels. 



" The moving potvers of the sanguiferous system are now to 

 be examined: first, those of the heart, by far the greatest of all; 

 afterwards, those which are only subsidiary, though indeed highly 

 useful. 



" That the powers of the heart cannot be accurately calculated 

 is clear, upon reflecting that neither the volume of blood pro- 

 jected at each pulsation, nor the celerity nor distance of its 



z " J. N. Weiss, De Dextro Cordis Ventriculo POST MORTEM ampliori. Altorf, 

 1767. 4to." 



a " Ant. Chaum. Sabatier, E. in vim Animdibus Ventriculorum Cordis eadem 

 Capacitas. Paris, 1772. 4to." 



b " Sam. Aurivilius, De Vasorum Pulmonal. % Cavitat. Cordis inequdi AmpH- 

 tudine. Getting. 1750. 4to." 



