KNOWLEDGE IN ANCIENT TIMES 15 



blood to the heart, and he knew that it carried something 

 to the heart and had an important part to play in altering 

 the character of the blood. He seems to have believed, 

 however, that it did not bring aerated blood to the heart 

 but air only, and that this air it drew from the cavities 

 of the lung. He regarded this vessel as a branch of the 

 arterial system, and it was on this account, recognising 

 the thin and vein-like character of its walls, that he called 

 it the venal artery. Galen paid very little attention to 

 the auricles, regarding them merely as dilatations at the 

 entry of the great veins into the heart. He therefore 

 described the heart as having only two cavities, the 

 two ventricles. The air carried by this pulmonary vein, 

 or venal artery, as he called it, entered, Galen thought, 

 the cavity of the left ventricle. There it met w r ith the 

 trickle of blood that came through the supposed channels 

 in the septum, and by its combination with this trickle 

 of blood of venous origin he believed that arterial blood 

 was produced. An important feature of the arterial 

 blood was the presence in it of a second kind of spirits, 

 the so-called vital spirits. These spirits, derived from 

 the heart, differed from the natural spirits derived from 

 the liver. The vital spirits were responsible for all kinds 

 of movement and muscular activity. Arterial blood 

 carrying its charge of vital spirits was distributed by 

 the arteries to all parts of the body. 



We need not, for our purposes, follow it there, but 

 we may glance for a moment at one group of arterial 

 branches that Galen considered were of special interest. 

 Some of the arterial blood naturally reached the brain, 

 where, according to Galen, it was charged with a third 

 kind of spirits, the animal spirits. These animal spirits, 

 like the other forms of spirits, Galen believed to be also 

 distributed to different parts of the body. The animal 

 spirits, however, were, it was thought, separated from the 



