78 Borelli and the Influence [lect. 



He discusses at length the resistance which the heart has 

 to overcome, resistance offered by the walls of the arteries them- 

 selves, by the tissues surrounding them, and by the minute and 

 variously shaped orifices through which the blood issues from 

 the terminations of the arteries in the several tissues. And 

 by a series of mathematical calculations he comes to the con- 

 clusion that the heart in maintaining the circulation has at each 

 beat to exert a force equivalent to not less than 135,000 lbs. 



His view of the flow in the arteries is worth giving in his 

 own words: 



" In the first place we must disprove the common assertion 

 " that blood is driven through the terminal orifices of the 

 "arteries after the fashion of a fountain, simply by the pro- 

 " pulsive force of the heart. 



11 The arteries are soft, distensible tubes full of blood, but as 

 " we have shewn not filled to extreme distension ; and during 

 "each, beat of the heart there is driven into them by the con- 

 striction of the heart, acting like a piston, a mass of blood 

 " sufficient to complete their distension or even more than 

 "sufficient, in which case the surplus is discharged beyond 

 " the arteries by the beat of the heart itself. But so soon 

 "as the beat is over the arteries return from their distended 

 "condition to the same soft and shrunken state in which they 

 " were before the beat. Therefore there must have escaped 

 "from them the mass of blood or the surplus of that mass 

 " which had been driven into them by the piston of the heart. 

 " But the blood which has been driven into the arteries cannot 

 " issue from them of its own accord through the extremely 

 "minute terminal orifices of the arteries since it possesses no 

 "force of its own. Nor is it driven out by the propulsion of 

 " the piston of the heart or only partly so since the arteries are 

 " not rigid tubes made of steel but are soft, and the force of the 

 " heart in its direct action is spent in expanding them, which 

 " expansion acts as a cause of retention rather than of expulsion 

 "of the blood." 



After shewing that the flow of blood out of the arteries 

 cannot be due to gravity, or to any force supplied by a 

 rarefaction of the blood he goes on : 



