8 



PRINCIPLES OF ANIMAL BIOLOGY 



revered teacher Sylvius, himself an anatomist of high reputation. Vesa- 

 lius was charged with all sorts of crimes, from being godless and sordid 

 to dissecting men alive. This persecution finally drove him to resign 

 his professorship, after which he was physician to Emperor Charles 

 V. Upon the succession of the less liberal Philip II, Vesalius found small 

 opportunity for creative work. He left the court and tried to regain 

 his old post at the university but died on a journey to Jerusalem before 

 the appointment was made. His ideas of anatomy, and particularly 

 of the functions of the organs, were not wholly correct. Some of them 



were borrowed from Galen, whom 

 he still admired, and now seem 

 absurd. His great contribution 

 was his overthrow of authority 

 and his return to firsthand obser- 

 vation as the basis of knowledge. 



Harvey and the Circulation of 

 the Blood. — One of the sharpest 

 reactions against the authority of 

 antiquity, and one of the most 

 hotly contested, was the recogni- 

 tion of the circulation of the blood. 

 Against the prevailing early view 

 that the arteries conveyed air, 

 Galen had held that they carried 

 blood; but he was never clear how 

 the arterial blood became converted 

 into venous blood, and in the veins 

 he definitely supposed the blood 

 to flow in both directions alternately. His views on this question 

 were still accepted in the sixteenth century. 



The first recognition that the entire course of the blood is a circulation 

 is found in the works of William Harvey (1578-1G57) (Fig. 4), of England. 

 He proved that the wall of the heart is muscular and that its contraction 

 drives the blood forward into the arteries; in the old theory the heart 

 was regarded as passive. By a simple calculation he demonstrated that 

 the quantity of blood passing through the heart in a very short time 

 exceeded the weight of the whole body and reasoned that new blood could 

 not be produced at such a rate. He showed by the swelling of the veins 

 below a ligature, and by the point of exit of blood at a wound, that blood 

 flows toward the heart in veins and away from it in arteries. He con- 

 cluded as a logical necessity that there must be a connection between 

 arteries and veins, but without a microscope he could never visually 

 demonstrate the capillaries. 



Fig. 4.— William Harvey, 1578-1657 

 {From Garrison, "History of Medicine.") 



