MOTION OF THE HEART AND BLOOD 



blood. This may not seem of much importance. Respira- 

 tory function, however, would suffer, and this would be 

 of no little significance T Again, a little later: ''Another 

 serious inconvenience would follow if our Maker had 

 not provided these valves, the blood would move back- 

 wards during expirations'^ So, in the nth chapter, 

 he concludes: "// seems that all these valves have a 

 common function in preventing regurgitation, ap- 

 propriate to both directions, one set leading away from 

 the heart and preventing return by that route, the other 

 leading into the heart and preventing escape from it. 

 Nature never wished to fatigue the heart with useless 

 work, neither bringing anything unnecessarily to it, nor 

 taking anything unnecessarily from it. Thus there are 

 four openings, two in each ventricle, one of which leads 

 into the heart, the other out of it.'' A bit farther on: 

 ^'One of the blood-vessels fastened on the heart has a 

 simple tunic, the other leading from it has a double 

 tunic. (Galen is referring to the right ventricle, but 

 the same things apply to the left.) The same cavity 

 being provided for both of these, blood enters through the 

 former and leaves through the latter." 



Galen proposes this argument to explain the 

 passage of blood from the vena cava through the 

 right ventricle to the lungs. By merely changing 

 the terms, we may apply it more properly to the 

 transfer of blood from the veins through the heart 

 to the arteries. From the words of that great Prince 

 of Physicians, Galen, it seems clear that blood filters 

 through the lung from the pulmonary artery to the 



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