34 Harvey and the [lect. 



" not on the near side of the ligature. But exactly the contrary 

 " ought to happen if the movement of the blood and the spirits 

 "took place in the direction from the viscera to all parts of 

 "the body. When a channel is interrupted, the flow beyond 

 " the interruption ceases ; the swelling of the veins therefore 

 "ought to be on the near side of the ligature. 



" Here is the solution of the doubt arising from what Aris- 

 " totle writes concerning sleep when he says : ' It is necessary 

 " ' that what is evaporated should be driven to some place and 

 " ' then be turned back and changed like Euripus. For the heat 

 " ' of every living thing ascends by nature to a higher place, 

 " ' but when it has reached the higher place, it in many cases 

 " ' turns back again and is carried downwards.' This is what 

 " Aristotle says. Now to explain this passage we must recognize 

 " the following. The passages of the heart are so arranged by 

 " nature that from the vena cava a flow takes place into the 

 " right ventricle, whence the way is open into the lung. From 

 "the lung moreover there is another entrance into the left 

 " ventricle of the heart, from which then a way is open into the 

 " aorta artery, certain membranes being so placed at the mouths 

 " of the vessels that they prevent return. Thus there is a sort 

 " of perpetual movement from the vena cava through the heart 

 "and lungs into the aorta artery as I have explained in my 

 " Peripatetic Questions. 



" Now when we are awake the movement of the native heat 

 "takes place in a direction outwards, namely, to the sensory 

 " regions of the brain. When we are asleep however it takes 

 " place in the contrary direction towards the heart. We must 

 " therefore conclude that when we are awake a large supply of 

 " blood and of spirits is conveyed to the arteries and thence to 

 " the nerves. When we are asleep however the same heat is 

 " carried back to the heart not by the arteries but by the veins. 

 " For the natural entrance into the heart is furnished by the 

 " vena cava, not by the arteries. A proof of this may be seen in 

 " the pulses, which when we are wide awake are full, vehement, 

 " quick, with a certain rapidly repeated vibration, but when we 

 "are asleep are small, languid, slow and infrequent. For in 

 " sleep the supply of native heat to the arteries is diminished, 



