METHODS OF PHYSIOLOGICAL RESEARCH 11 



pneuma. The psychical (animal) functions comprise thinking, feel- 

 ing, and voluntary motion ; the sphygmical (vital) functions, the 

 heart-beat, the pulse, and the production of heat ; the 2^^^ysical 

 (natural) functions, nutrition, growth, secretion, and reproduction 

 with its related activities. The blood is formed in the liver, and 

 the veins arise there. Through the veins the blood goes to the 

 right ventricle of the heart, where the useful part is separated 

 from the useless ; the former is carried to the left ventricle, while 

 the latter goes through the pulmonary artery to the lungs. In 

 the lungs, the useless part is regenerated by the spirits and made 

 useful. It is remarkable with what prophetic gift Galen pointed 

 to a constituent of the air as the spirits, the nature of which he 

 could not yet divine. He expresses clearly the supposition that 

 it will be possible at some time to isolate that constituent of the 

 air that forms the spirits. More than fifteen hundred years elapsed 

 before Galen's supposition was confirmed by the discovery of 

 oxygen by Priestley and Lavoisier. The blood, regenerated by the 

 receipt of spirits in the lungs, flows through the pulmonary veins 

 into the left heart, whence, together with the rest of the useful 

 blood, it is carried by the aorta and its branches throughout the 

 whole body. Galen's views upon the nervous system are equally 

 interesting. In the brain and the spinal cord are the origins of 

 the sensory and the motor activities of the nerves. The motor 

 nerves act by pulling like a string upon the motor organs. In the 

 special physiology of nerves, Galen investigated particularly the 

 action of the vagus and the intercostal nerves upon respiration and 

 the action of the heart, and he cut the spinal cord transversely 

 and longitudinally — experiments which show how deeply he had 

 penetrated into an understanding of the mutual relations of the 

 individual organs of the body. 



Galen's physiological system was for that time a monumental 

 work, and the fact that Galen's views continued for thirteen 

 hundred j^ears as the unassailable code of medicine is surely not 

 to be ascribed simply to the decay of the ancient culture and 

 to the complete barrenness of the middle ages in scientific matters. 

 The development of physiological investigation took not a single 

 step forward during the middle ages. The Arabians, who had 

 come to possess the ancient culture, were, indeed, prominent as 

 physicians, but Islam forbade them alike independent investigation 

 and philosophical thought. Even Avicenna (Ibn Sina, 980-1037), 

 who was the most prominent of the Arabian physicians and 

 showed philosophical tendencies, performed no original work. 

 With slight changes his system was the system of Galen, whose 

 glory he obscured by his own powerful authority in the civilised 

 world of that time. Moreover, the many famous medical schools 

 which arose at that time in Italy, France, and Spain trained many 

 able physicians, but did not advance beyond Galen's ideas, not- 



