SCIENCE OF THE ROMAN PERIOD 



nerves. He had rightly pointed out that nerves were 

 merely connections between the brain and spinal-cord 

 and distant muscles and organs, and had recognized 

 that there were two kinds of nerves, but his explana- 

 tion of the action of these nerves was that "nervous 

 spirits" were carried to the cavities of the brain by 

 blood-vessels, and from there transmitted through the 

 body along the nerve-trunks. 



In the human skull, overlying the nasal cavity, there 

 are two thin plates of bone perforated with numerous 

 small apertures. These apertures allow the passage 

 of numerous nerve-filaments which extend from a group 

 of cells in the brain to the delicate membranes in the 

 nasal cavity. These perforations in the bone, there- 

 fore, are simply to allow the passage of the nerves. 

 But Galen gave a very different explanation. He be- 

 lieved that impure "animal spirits" were carried to 

 the cavities of the brain by the arteries in the neck 

 and from there were sifted out through these perforated 

 bones, and so expelled from the body. 



He had observed that the skin played an important 

 part in cooling the body, but he seems to have be- 

 lieved that the heart was equally active in overheating 

 it. The skin, therefore, absorbed air for the purpose 

 of "cooling the heart," and this cooling process was 

 aided by the brain, whose secretions aided also in the 

 cooling process. The heart itself was the seat of cour- 

 age ; the brain the seat of the rational soul ; and the liver 

 the seat of love. 



The greatness of Galen's teachings lay in his knowl- 

 edge of anatomy of the organs ; his weakness was in his 

 interpretations of their functions. Unfortunately, sue- 



283 



