704 PHILOSOPHICAL TRANSACTIONS. [aNNO 1702. 



blood meets with in its progress through the vessels, shall be made, the remain- 

 ing force will he found so exceedingly weak, that to propel the blood through 

 the veins, may be a task alone too great for so small a power, without charging 

 it with the additional ditficulty of forcing the muscles of the heart. 



Borelli calculates the force of the heart, and the muscular coat of the arteries, 

 to be together equal to a weight of 3,750 lb. and allots them a resistance equal 

 to 1 80,000 lb. ; to overcome which, is 45 to 1. To make up for a dispropor- 

 tion, by his own confession, incredible to those who have not considered the 

 matter as he had done, he flings into the scale the additional force of percussion, 

 which he leaves indefinite, and thinks sufficient to force any quiescent finite 

 resistance whatever. But though the hypothesis of Borelli may in this case be 

 found precarious or insufficient, his theory still holds good ; at least it ought to 

 be allowed in justice to his great abilities and exactness, till he is convicted of 

 some material error in his calculations, which has not as yet been done by any 

 one that I know of. 



Supposing then the force of the heart, and of the muscular coat of the arte- 

 ries, as likewise of the resistance which they must overcome, to be computed 

 with any degree ot accuracy ; there remains yet such a prodigious disproportion 

 to be accounted for, as requires some more powerful agent than any yet assigned, 

 to make up the deficiency. What assistance the heart receives from the action 

 of the thorax towards facilitating its contraction, without whicii assistance there 

 could have been no systole, has been already shown ; but neither the intercostal 

 muscles, nor diaphragm, which are so instrumental in that part of its action, 

 can contribute any thing to the diastole, because they serve only to enlarge the 

 cavity of the thorax, and thereby to open a passage to the blood from the heart 

 and promote its constriction. 



Whatever therefore the force is, that dilates the heart, and is the cause of 

 the diastole, it must be equal to that of the heart, the intercostal muscles, and 

 the diaphragm : to all which it acts as jan antagonist. I take no notice of the 

 serratus major anticus, and other muscles, which have an obscure share in the 

 elevation of the costae, because as much may reasonably be deducted on the 

 account of the obliquus externus abdominis, and other muscles ; which, having 

 their insertions on some of the lower ribs, are as instrumental towards the 

 depression of them, and so balance the account. But the chief use of these 

 is in violent respiration ; in ordinary respiration, their share is small. 



Such a real power, which ma) in the least be suspected of any share in this 

 action, is difficult, perhaps impossible, to be found in the machine of any animal 

 body, and yet without some such antagonist it is as impossible that the circula- 

 tion of the blood should be maintained. All the engines yet discovered within 



