702 PHILOSOPHICAL TRANSACTIONS. [aNNO 1702. 



that of a syringe, whose extremity is immersed in water, the enlargement or 

 expansion of the channels of the artery answering to the drawing of the em- 

 bolus, as the constrictive motion of the muscle of the heart does to the pressure 

 ot the atmosphere on the surface of the water, the one making way for the 

 fluid, and the other forcing it to follow, where the resistance is least. In this 

 sense we may allow a sort of attraction to the pulmonary artery, depending 

 wholly on the action of the intercostal muscles and diaphragm, which we must 

 therefore confess is very serviceable and instrumental in promoting the systole 

 of the heart. 



But if the learned author be deficient in his account of the systole ; that is, 

 if he has not observed all the mechanism and contrivance of nature for the con- 

 traction of the heart, much less sufficiently has he accounted for the diastole, 

 or dilatation of it, which he ascribes to a motion of restitution of the over- 

 strained fibres, which yet he confesses are made for constriction only. It is 

 true, he immediately after joins the influx of the blood as a concurrent cause ; 

 but from the slight notice that he takes of it, it is plain, that he did not so 

 much as dream of any great share it had in that action. 



But, if contraction be the sole action of these fibres, as indeed it is of 

 all muscular fibres, I wonder how so judicious a writer came to slip into such 

 an absurdity, as to call their distension a motion of restitution. For from the 

 nature of those fibres, and their disposition in the structure of the heart, the 

 natural state of the heart appears manifestly to be tonical, and its dilatation a 

 state of violence ; and consequently the constriction is the true motion of resti- 

 tution, and the state to which it will spontaneously return, when the force is 

 taken off, which is the work of the intercostal muscles and diaphragm. 



Thus we are left still to seek for the true cause of the diastole, which seems 

 to be the main and most difficult phenomenon, relating to the heart and the 

 circulation of the blood. But in Mr. Cowper's ingenious Introduction to his 

 Anatomy of Human Bodies, I find the share which Dr. Lower hints the blood 

 to have in that action, further prosecuted, and improved into the main instru- 

 ment of the dilatation of the heart, wherein I agree entirely with him. But as 

 to the manner and reasons of its being so very instrumental, I cannot be so per- 

 fectly of his mind. "The heart of an animal," says Mr. Cowper, " bears a 

 great analogy to the pendulums of those artificial automata, clocks and watches, 

 whilst its motion is performed like that of other muscles, the blood doing the 

 office of a pondus." 



By the blood's doing the office of a pondus, I suppose he means, that the 

 blood contributes in the same manner to the motion of the heart, as the weights 

 do to that of the pendulum of a clock. If so the blood, according to him, 



