180 BIOLOGY AND ITS MAKERS 
Among the ancient physiologists the great Roman phy- 
sician Galen is the most noteworthy figure. As he was the 
greatest anatomist, so he was also the greatest physiologist 
of ancient times. All physiological knowledge of the time 
centered in his writings, and these were the standards of 
physiology for many centuries, as they were also for anatomy. 
In the early days anatomy, physiology, and medicine were all 
united into a poorly digested mass of facts and fancies. This 
state of affairs lasted until the sixteenth century, and then the 
awakening came, through the efforts of gifted men, endued 
with the spirit of independent investigation. The advances 
made depended upon the work or leadership of these men, 
and there are certain periods of especial importance for the 
advance of physiology that must be pointed out. 
Period of Harvey.—The first of these epochs to be espe- 
cially noted here is the period of Harvey (1578-1657). In his 
time the old idea of spirits and humors was giving way, but 
there was still much vagueness regarding the activities of the 
body. He helped to illuminate the subject by showing a con- 
nection between arteries and veins, and by demonstrating 
the circulation of the blood. As we have seen in an earlier 
chapter, Harvey did not observe the blood passing through 
the capillaries from arteries to veins, but his reasoning was 
unassailable that such a connection must exist,and that the 
blood made a complete circulation. He gave his conclusions 
in his medical lectures as early as 1619, but did not publish 
his views until 1628. It was reserved for Malpighi, in 1661, 
actually to see the circulation through the capillaries under 
the microscope, and for Leeuwenhoek, in 1669 and later 
years, to extend these observations. 
It was during Harvey’s life that the microscope was 
brought into use and was of such great assistance in advanc- 
ing knowledge. Harvey himself, however, made little use 
of this instrument. It was during his life also that the knowl- 
