in] of the New Physics. 77 



" between the . base and the apex ; but other external fibres 

 "surrounding the obliquely transverse ones and intersecting 

 " them in a decussating manner prevent, as we shall presently 

 "shew, their elongation and protuberance, whence necessarily 

 "the inflation of those fibres gives rise to an intumescence 

 "internally towards the cavities and so the inflated internal 

 " sides of the walls are brought nearer to each other." 



We have seen that an important link in Harvey's argument 

 was furnished by his calculations as to the quantity of blood 

 driven into the arteries from the heart, calculations which were 

 as we shall see repeated in a more exact manner some years 

 later by Richard Lower. Borelli goes further, he is anxious to 

 determine in mechanical terms the force of the ventricular 

 systole. Assuming that the force of contraction of all healthy 

 muscular tissue is the same for a unit of bulk, and observing 

 that the ' fleshy mass of the heart ' is in bulk equal to a 

 masseter and temporal muscle combined, he concludes that 

 it exercises the same force as these two together, which 

 force can be determined experimentally. He finds that the 

 muscles of the two sides of the jaw acting together can support a 

 weight of more than 300 lbs. The muscles of one side therefore 

 will support a weight of more than 150 lbs. But this is an 

 instance of the partial force of a mnscle ; if we want to find the 

 whole force of the muscle we ought to multiply this result at 

 least 20 times. Thus he reaches the conclusion that the 

 motive force of the heart considered by itself may be calculated 

 as equal to that of supporting a weight of more than 3000 lbs. 



Perhaps the most interesting part of Borelli's work on 

 the circulation is his treatment of the flow in the arteries. 

 Working on the lines of his view that the action of the heart 

 is tq be likened to the action of a piston in a pump, he argues 

 that at the close of a heart-beat the arteries are not empty, 

 but still hold a considerable quantity of blood ; according to his 

 calculations they contain about \ of the total blood of the body, 

 the quantity introduced at a single beat, namely about three 

 ounces, being a twentieth part of that, and occupying a space 

 in the arteries next to the heart not more than half a foot in 

 length. 



