112 SEVENTEENTH CENTURY. FT. in. 



Therefore it was clear that the blood in the vein was flowing 

 from the leg to the heart, and was stopped from flowing up- 

 wards by the bandage. When he tied an artery and a vein 

 in the arm the same thing happened ; the blood in the 

 artery was flowing towards the hand, while in the vein it was 

 Rowing fr0m the hand towards the heart. 



This led Harvey to suspect that the blood is always 

 making a continuous journey round and round, first out of 

 the heart through the arteries to all parts of the body, and 

 then back through the veins to the heart again. And now 

 the use of the little valves became evident. While the blood 

 flows, as it should do, towards the heart, they lie open and 

 offer it no resistance, but directly anything drives it in the 

 wrong direction they close at once, and prevent it from 

 flowing backwards. The throbbing of the arteries was also 

 explained by this theory, for the blood being pumped into 

 them by a regular movement of the heart, they swell at each 

 rush of blood, and contract again before the next, and so 

 rise and fall in exact time with the beating of the heart. 



Harvey also found that Caesalpinus and his contempo- 

 raries had been right in suspecting that the blood makes a 

 small circuit from the heart through the lungs and back 

 again. We will try to understand all this with the assistance 

 of a diagram, which, however, you must remember is only 

 to help you, and not a real drawing of the parts. Starting 

 from the left lower chamber a of the heart, the blood is 

 pumped out of the left top corner of this chamber into an 

 artery in the direction of the arrow i. This artery soon 

 divides into two branches, one going downwards by the 

 arrow 2 to the lower part of the body, the other upwards by 

 the arrow 2' to the arms and neck ; and, after flowing into 

 the different parts of the body, the blood in the lower artery 



