CHAPTER XIV 



THE DISCOVERY OF THE CIRCULATION OF THE BLOOD 



I. Harvey's Predecessors 

 Galen s system of blood-movement 



BIOLOGICAL RESEARCH Under the Renaissance, as the above narrative 

 shows, considerably widened the knowledge of animate nature. The 

 progress achieved was particularly great in the anatomical sphere- 

 Vesalius and his school contributed not only to human, but also to animal 

 anatomy a wealth of new facts which put the knowledge of classical antiquity 

 completely in the shade. But as regards their general conception of nature 

 these research-workers remained entirely on the ground that had been broken 

 by Aristotle and Galen. Now, however, these newly-won facts could not be 

 reconciled to the old system; the same thing had happened to Copernicus 

 and Galileo in regard to astronomy. A definite break away from the ancient 

 ideas of life was inevitable. In one field in particular was the influence of the 

 ancient system fated - regarding the idea of the movement of the blood in 

 the body and its importance to life. Hippocrates, Aristotle, and Galen had 

 all held the same views on the heart and the vessels of the body in so far as 

 they took the most important qualities of the blood to be the "vital spirits" 

 which it was thought to contain; and in face of the speculations on these 

 spirits the study of the movements of the blood in the veins was sadly 

 neglected. Galen, who among the biologists of antiquity had the richest 

 experimental material at his disposal, had worked up into a systematic 

 whole all the knowledge of the vascular system which classical antiquity 

 had accumulated. He had, as will be remembered, succeeded in destroying the 

 old illusion that the arteries and the left ventricle of the heart contained air; 

 he found in them a kind of blood which he believed to have acquired its' 

 light-red colour from the pneuma, the half-mysterious life-spirit, which it 

 contained. The pneuma was conveyed to the blood in the arteries from the 

 air, which was introduced by inhalation into the lungs and thence to the 

 left ventricle of the heart. The non-pneuma-conveying blood — the venous 

 blood — had its centre in the liver, where it was formed out of food from 

 the digestive canal. From the liver the blood was conveyed through the 

 veins partly out into the body, in which it was converted, by a process that 

 was not very clearly explained, into "flesh,;* and partly to the right heart- 



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