CIRCULATION OF THE BLOOD 8 



arteries arc filled and distended by the blood forced into 

 them by the contraction of the ventricles ; the arteries, there- 

 fore, are distended, because they are filled like sacs or blad- 

 ders, and are not filled because they expand like bellows. It 

 is in virtue of one and the same cause, therefore, that all 

 the arteries of the body pulsate, viz., the contraction of the 

 left ventricle; in the same way as the pulmonary artery 

 pulsates by the contraction of the right ventricle. 



Finally, that the pulses of the arteries are due to the 

 impulses of the blood from the left ventricle, may be illus- 

 trated by blowing into a glove, when the whole of the 

 fingers will be found to become distended at one and the 

 same time, and in their tension to bear some resemblance 

 to the pulse. For in the ratio of the tension is the pulse of 

 the heart, fuller, stronger, and more frequent as that acts 

 more vigorously, still preserving the rhythm and volume, 

 and order of the heart's contractions. Nor is it to be 

 expected that because of the motion of the blood, the time 

 at which the contraction of the heart takes place, and that 

 at which the pulse in an artery (especially a distant one) is 

 felt, shall be otherwise than simultaneous: it is here the 

 same as in blowing up a glove or bladder; for in a plenum (as 

 in a drum, a long piece of timber, etc.) the stroke and the 

 motion occur at both extremities at the same time. 

 Aristotle, 1 too, has said, "the blood of all animals palpitates 

 within their veins (meaning the arteries), and by the pulse 

 is sent everywhere simultaneously." And further,* "thus 

 do all the veins pulsate together and by successive strokes, 

 because they all depend upon the heart; and, as it is always 

 in motion, so are they likewise always moving together, but 

 by successive movements." It is well to observe with 

 Galen, in this place, that the old philosophers called the 

 arteries veins. 



I happened upon one occasion to have a particular case 

 under my care, which plainly satisfied me of the truth: A 

 certain person was affected with a large pulsating tumour on 

 the right side of the neck, called an aneurism, just at that 

 part where the artery descends into the axilla, produced by 

 an erosion of the artery itself, and daily increasing in size; 



1 Oe Anim., iii, cap. 9. DC Rcspir., cap. 20. 



