700 PHILOSOPHICAL TRANSACTIONS. [aNNO 1702. 



perplexed to find out its cause. Dr. Lower's account of the systole, however 

 solid and ingenious, has something deficient, and his hypothesis of the diastole 

 seems precarious and false ; for having by sound arguments, drawn from the 

 structure and mechanism of the heart, established the certainty of its muscular 

 motion, he rests satisfied, without taking notice of any assistance that the heart 

 receives from any other part, except from the brain, by means of the eighth 

 pair of nerves. 



Borelli, in his QEconomia Animalis, computes the motive power of the ma- 

 chine of the heart to be equal to, or to surmount, that of the weight of 3000 

 pounds : the obstacles to the motion of the blood through the arteries he 

 esteems equivalent to 180,000lb: which is6o times as much as he rates the force 

 of the heart at : then deducting 45,000 lb. for the adventitious help of the mus- 

 cular elastic coat of the arteries, he leaves the heart with a force of 3000 lb. to 

 overcome a resistance of 135,000 lb., that is, with 1 to remove 45. This 

 stupendous effect he contents himself with ascribing to the energy of percus- 

 sion. But had he proceeded in his calculation to the veins, which he allows to 

 contain constantly a quantity of blood, quadruple to the contents of the arteries, 

 and to which this energy of percussion does either not reach at all, or but very 

 languidly, he might probably have seen a necessity for some other expedient, to 

 remove so insuperable a difficulty. But not to insist rigorously on the exact- 

 ness of this calculation, we may allow a much greater deduction than would 

 be justifiable, without lessening the difficulty. But this account I have taken 

 notice of purely for the sake of the calculation, which may be of use in the 

 sequel ; the account itself being inother respects more defective than Dr. Lower's, 

 to which we will return. 



The Doctor appears to have overlooked something of very great moment and 

 importance, in the explanation of the action of the heart : for though it should 

 be granted, that the muscular fibres of the heart, acted on by the nerves, are 

 the immediate instruments of its constriction or systole, yet it must not be 

 denied, that the intercostal muscles and diaphragm are of great service to aid 

 and facilitate this contraction, by opening a passage for the blood through the 

 lungs, which denied, would be an invincible obstacle. 



Nor do they promote it that way only : the manner in which they farther 

 assist the heart in its contraction, will appear manifestly, if we consider the 

 different posture, situation, and capacity of the blood vessels of the lungs, in 

 the several times of elevation and depression of the costa;. The pulmonary 

 artery rises from the right ventricle of the heart, and runs in one trunk, till it 

 comes to the aspera arteria, where it is divided, and sends a bianch along with 

 each division of the aspera arteria, accompanying all the bronchia, in their 



