48 BIOLOGY AND ITS MAKERS 



out that this is the first time that quantitative determinations 

 were introduced into physiology. 



Views of His Predecessors on the Movement of the Blood. 

 Galen's view of the movement of the blood was not com- 

 pletely replaced until the establishment of Harvey's view. 

 The Greek anatomist thought that there was an ebb and flow 

 of blood within both veins and arteries throughout the 

 system. The left side of the heart was supposed to contain 

 blood vitalized by a mixture of animal spirits within the lungs. 

 The veins were thought to contain crude blood. He sup- 

 posed, further, that there was a communication between the 

 right and the left side of the heart through very minute pores 

 in the septum, and that some blood from the right side passed 

 through the pores into the left side and there became charged 

 with animal spirits. It should also be pointed out that Galen 

 believed in the transference of some blood through the lungs 

 from the right to the left side of the heart, and in this fore- 

 shadowed the views which were later developed by Servetus 

 and Realdus Columbus. 



Vesalius, in the first edition of his work (1543) expressed 

 doubts upon the existence of pores in the partition-wall of 

 the -heart through which blood could pass ; and in the second 

 edition (1555) of the Fabrica he became more skeptical. 

 In taking this position he attacked a fundamental part of 

 the belief of Galen. The careful structural studies of Vesalius 

 must have led him very near to an understanding of the con- 

 nection between arteries and veins. Fig. n shows one of 

 his sketches of the arrangement of arteries and veins. He 

 saw that the minute terminals of arteries and veins came very 

 close together in the tissues of the body, but he did not grasp 

 the meaning of the observation, because his physiology was 

 still that of Galen; Vesalius continued to believe that the 

 arteries contained blood mixed with spirits, and the veins 

 crude blood, and his idea of the movement was that of an 



