ON THE MOTION OF THE BLOOD. 77 



centa (127), and from experiments instituted on living 

 animals. We formerly mentioned the muscular ap- 

 pearance in the extreme veins near the heart (95). (H) 

 133. These are the chief powers which move the 

 blood and depend upon the structure and vitality of the 

 sanguiferous system : we say nothing of the effect of 

 gravity, attraction, and other powers, common to all 

 matter. The more remote assistance derived after 

 birth from particular functions, v. c. respiration and 

 muscular motion, will appear in our account of those 

 functions. 



NOTES. 



(A) Dr. W. Hunter first accounted for this in 1746. 



" The systole and diastole of the heart, simply, could not pro- 

 duce such an effect ; nor could it have been produced, if it had 

 thrown the blood into a straight tube, in the direction of the axis 

 of the left ventricle, as is the case with fish, and some other 

 classes of animals : but by throwing the blood into a curved tube, 

 viz. the aorta, that artery, at its curve, endeavours to throw itself 

 into a straight line, to increase its capacity ; but the aorta being 

 the fixed point against the back, and the heart in some degree 

 loose and pendulous, the influence of its own action is thrown 

 upon itself, and it is tilted forwards against the inside of the 

 chest." * 



Dr. Barclay has the following passage on this point. 



" When the blood is forced into the arteries, their curvatures, 

 near where they issue from the ventricles, are from their disten- 

 tion lengthened and extended towards straight lines ; and, caus- 

 ing the heart to participate in their motions, compel it to describe 



* Treatise on the Blood, &c. by John Hunter, p. 146. Note. 



