12 CIRCULATION OF THE BLOOD 



destined to exercise the most profound influence on the 

 course of science. His name was Galen, and he became 

 one of the most eminent exponents of science in all 

 antiquity. Galen afterwards practised for many years 

 at Rome, and became the medical attendant to the 

 Roman Emperor, Marcus Aurelius. He died in the year 

 200 A.D. His account of the vascular system is of great 

 importance for our subject. 



Galen's views on the nature and action of the heart, 

 the blood-vessels, and the pulse remained current for 

 some fifteen hundred years, and all references to the 

 nature and action of the heart, the blood, or the pulse 

 in older English writers for example, in Chaucer or 

 Shakespeare can be traced to interpretations of Galen's 

 works. The ideas of Galen are therefore of more than 

 historical interest. An understanding of them is neces- 

 sary not only for the history of science, but also for 

 the explanation of many allusions in literature and not 

 a few colloquial expressions. We shall therefore turn 

 at once to a discussion of Galen's physiological views. 



Galen taught (Plate II.) that the body was governed by 

 three principal structures that formed a sort of aris- 

 tocracy among the organs of the body ; these were the 

 liver, the heart, and the brain. Ingested food passed 

 into the intestines and was absorbed from there as 

 chyle, and carried by the portal vessel to the liver. In 

 the liver this chyle was elaborated into blood, and 

 charged with an imaginary essence, the natural spirits. 

 The presence of these imaginary natural spirits was 

 supposed to be necessary for the continuance of even 

 the lowest form of life. 



The natural spirits were distributed from the liver to 

 the various parts of the body, and they were sent thither 

 by means of the veins. The liver was thus regarded by 

 Galen as the centre of the venous system. The veins 



