90 FATHERS OF BIOLOGY. 



(3) The veins in like manner return this blood in- 

 cessantly to the heart from all parts and members 

 of the body. 



As to the first proposition Harvey says, " Did the 

 heart eject but two drachms of blood on each contraction, 

 and the beats in half an hour were a thousand, the 

 quantity expelled in that time would amount to twenty 

 pounds and ten ounces ; and were the quantity an ounce, 

 it would be as much as eighty pounds and four ounces. 

 Such quantities, it is certain, could not be supplied by 

 any possible amount of meat and drink consumed within 

 the time specified. It is the same blood, consequently, 

 that is now flowing out by the arteries, now returning by 

 the veins ; and it is simply matter of necessity that 

 the blood should perform a circuit, or return to the place 

 from whence it went forth." 



Demonstration of the second proposition that the 

 blood enters a limb by the arteries and returns from it 

 by the veins is afforded by the effects of a ligature. 

 For if the upper part of the arm be tightly bound, the 

 arteries below will not pulsate, while those above will 

 throb violently. The hand under such circumstances 

 will retain its natural colour and appearance, although, if 

 the bandage be kept on for a minute or two, it will 

 begin to look livid and to fall in temperature. But 

 if the bandage be now slackened a little, the hand and 

 the arm will immediately become suffused, and the super- 



