n] Circulation of the Blood. 37 



"at once like a flood either to the feet, or to the hands and 

 "fingers, and becoming collected there. For this would give 

 i( rise to two evils ; on the one hand the upper parts of the 

 11 limbs would suffer from want of nourishment, and on the 

 "other the hands and feet would be troubled with a con- 

 tinual swelling. In order therefore that the blood should 

 " be everywhere distributed in a certain just measure and 

 " admirable proportion for maintaining the nourishment of 

 " the several parts, these valves of the veins were formed. 

 ******* 



"In the veins laid bare and examined untouched, these 

 " valves are visible to a certain extent. Nay more, that even in 

 " the living arm or thigh these valves may give evidence of their 

 " existence appears clearly from the fact that, when in letting 

 " blood the assistants bind the limbs, at intervals along the 

 " course of the veins, little knots as it were are seen from the 

 " outside ; these are swellings caused by the valves. 



yfc yfc $fc 9 ^ W W 



" That indeed the flow of the blood is slowed by means 

 " of these valves is not only made clear by their construction 

 " but also is shewn by the following experiment which anyone 

 " can make, either by laying bare the veins in a dead body, or 

 " by ligaturing a limb in a living body, as they do when they 

 " let blood. For if you attempt to press, or by rubbing to drive 

 " the blood downwards (towards the hand for instance) you 

 " will clearly see that its flow is prevented and delayed by 

 "the valves." 



But he wholly failed to recognize their true function. Still 

 labouring under the influence of the old doctrines and believing 

 that the use of the veins was that of carrying crude blood, 

 blood not vivified by the vital spirits, from the heart to the 

 tissues, he thought that he had fully explained the value of the 

 veins, by pointing out that they opposed the flow from the 

 heart to the tissues, not of all blood but only of an excess of 

 blood; their purpose was to prevent the blood as it flowed 

 along the veins from the heart being heaped up too much in 

 one place. But he also thought that they were the means of 

 furnishing temporary local reservoirs of blood ; and he likens 



