HISTORY OF THE VIEWS OF NERVOUS 



ACTIVITY 



By D. FRASER HARRIS, M.D., D.Sc, B.Sc. (Lond.), F.R.S.E. 



Professor of Histology and Physiology, Dalhousie University, Halifax, Nova Scotia 



It is always instructive to trace the growth of an idea, to be 

 able to watch the notion of something, even of so elusive a thing 

 as the nerve-impulse, grow gradually in clearness and in definite- 

 ness as the centuries roll on. 



The term "nerve-impulse" is of course wholly modern. It 

 would not be profitable to go farther back than the time when 

 the Greek philosophers imagined that the nerves were hollow 

 and conveyed " spirits " through the pores (poroi) of their 

 substance. 



The Alexandrine School of Greek Anatomy, founded as far 

 back as 300 b.c. by Ptolemy I., recognised the functional differ- 

 ence between sensory and motor nerves. The two best known 

 teachers in it — Herophilus and Erasistratus — devoted much 

 attention to the nervous system ; they dissected the nerves to 

 their origins in the brain and spinal cord, they displayed the 

 veins of the brain and investigated its cavities or ventricles, 

 believing that in the Fourth of these, in the Medulla Oblongata, 

 the soul was situated. The meeting place of the venous sinuses 

 of the coverings of the brain is still known as the Torcular 

 Herophili. The physiology taught by Claudius Galen of Rome 

 (131-200 a.d.) was an outgrowth of the Alexandrian. Galen had 

 the clearest conception of the nerve-trunks as merely conductors 

 of something — he called it spirits — to or from the brain and 

 spinal cord. The doctrine of spirits in general he elaborates so 

 as to recognise three kinds of spirits — natural, vital, and animal. 

 We can hardly understand the nerve physiology of the Middle 

 Ages without some notion of these three kinds of spirit. Briefly 

 it was this : the food in the intestine is absorbed into the portal 

 vein and goes to the liver, where it is worked up into blood 

 which is endowed with natural spirits, or, in modern language, 



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