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 leit 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. 11 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 
