50 MOTION OF THE 



of blood must be expelled, and a like proportion received with 

 each stroke of the heart, the capacity of the ventricle con- 

 tracted always bearing a certain relation to the capacity of the 

 ventricle when dilated. And since in dilating, the ventricles 

 cannot be supposed to get filled with nothing, or with an ima- 

 ginary something ; so in contracting they never expel nothing 

 or aught imaginary, but always a certain something, viz. blood, 

 in proportion to the amount of the contraction. "Whence it 

 is to be inferred, that if at one stroke the heart in man, the 

 ox or the sheep, ejects but a single drachm of blood, and there 

 are one thousand strokes in half an hour, in this interval there 

 will have been ten pounds five ounces expelled: were there with 

 each stroke two drachms expelled, the quantity would of course 

 amount to twenty pounds and ten ounces ; were there half an 

 ounce, the quantity would come to forty-one pounds and eight 

 ounces; and were there one ounce it would be as much as 

 eighty-three pounds and four ounces ; the whole of which, in 

 the course of one half hour, would have been transfused from 

 the veins to the arteries. The actual quantity of blood expelled 

 at each stroke of the heart, and the circumstances under which 

 it is either greater or less than ordinary, I leave for particular 

 determination afterwards, from numerous observations which 

 I have made on the subject. 



Meantime this much I know, and would here proclaim to 

 all that the blood is transfused at one time in larger, at an- 

 other in smaller quantity ; and that the circuit of the blood is 

 accomplished now more rapidly, now more slowly, according to 

 the temperament, age, &c. of the individual, to external and 

 internal circumstances, to naturals and non-naturals, sleep, 

 rest, food, exercise, affections of the mind, and the like. But 

 indeed, supposing even the smallest quantity of blood to be 

 passed through the heart and the lungs with each pulsation, a 

 vastly greater amount would still be thrown into the arteries 

 and whole body, than could by any possibility be supplied by 

 the food consumed ; in short it could be furnished in no other 

 way than by making a circuit and returning. 



This truth, indeed, presents itself obviously before us when 

 we consider what happens in the dissection of living animals ; 

 the great artery need not be divided, but a very small branch 

 only, (as Galen even proves in regard to man,) to have the whole 



