HARVEY'S WORK 53 



times the body weight of a heavy man. Where can all 

 this blood come from ? Where can it all go to ? We 

 know that the valves at the root of the great arteries 

 prevent it regurgitating. It cannot come from the in- 

 gested food and drink, for no one could consume so much 

 in one hour ! It cannot go to and remain in the tissues, 

 for they would soon all burst and ooze with blood ! 



9. But if all this blood is sent out by the arteries into 

 the body, and if the body itself is not large enough to 

 supply it, where does it come from ? It must come from 

 the veins, which also contain blood. This conclusion 

 is reinforced by a very simple piece of knowledge. The 

 proportion of the weight of the blood to that of the rest 

 of the body is known, and it is well known too that if an 

 artery of any size is cut, and no remedies applied, we should 

 bleed to death in a very short time. The bleeding would 

 get slower and slower until it finally ceased as the blood 

 was exhausted and death approached. The reason must 

 be that the blood, being lost, does not reach the veins 

 and so cannot return again from them to the arteries. 

 Blood does not escape in the same rapid way from severed 

 veins, because their walls are flabby and have little muscle 

 or propelling power. 



10. But how does this blood get from the venous 

 system to the left side of the heart ? And how, too, does 

 it get from the arteries into the veins ? These are the 

 crucial questions in the whole discussion. We know the 

 answers to them now. Let us see how Harvey sought 

 to answer them. 



Blood can enter the right auricle through the vena 

 cava, the opening of which into the right auricle is patent 

 and obvious. It can then enter the right ventricle, the 

 opening into which from the right auricle is equally 

 obvious, though guarded by valves. Regurgitation 

 through this auriculo-ventricular orifice is prevented 



