ABSTRACT
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 William Harvey https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203704929/d410b27e-9bec-4300-a13c-e317203e46bd/content/fig1_14_6.jpg"/> George Louis Leclerc de Buffon https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203704929/d410b27e-9bec-4300-a13c-e317203e46bd/content/fig1_14_7.jpg"/> 109chamber, from which "soot" was given off through the pulmonary arteries; the wall between the right and the left ventricles was full of fine pores, through which the blood oozed from the right to the left side, to be "leansed" by the action of the pneuma. Galen had but vague ideas as to the movement of the blood in the vessels; in the veins, at any rate, the blood moved, according to his notion, alternately in both directions. Such was Galen's theory of the blood-vessels and their contents, and in this form it was still accepted by the great anatomists of the sixteenth century. All its vagueness and many contradictions would undoubtedly have been realized long before had not the blood-vessel system of old been considered the very centre of life itself; the mysterious pneuma was only one side of this blood's specific life-content; the different kinds of soul that man was believed to possess — the "vegetative," with the liver as its organ, and the "animal" in the heart — were also intimately connected with the blood and through it affected the entire body. 1 Speculation about these components in the organism certainly did not make the conception of the vascular system any clearer; moreover, it entailed the risk that any critical discussion of these organs might be interpreted as an attempt to call into question the immortal soul of man, which would inevitably have involved the scientific student in trouble with the theologians and the Inquisition. Typical in this respect is Vesalius's attitude regarding the pores in the dividing wall between the right and the left heart-chambers; he could not find any trace of them, but cautiously adds that all the same the blood might perhaps be able to ooze through the wall itself. His pupils adopted the same cautious attitude on this point, particularly Fabrizio, the discoverer of the venous valves.
