2 C. A. G. WIERSMA 



Weber in 1845 were convinced that stimulation of the vagus stopped or 

 slowed the heart. Several other more peripheral phenomena, such as inliibition 

 of the intestinal musculature by splanchnic stimulation were brought under 

 the same heading. But very httle attention was given to the possibility that 

 centrally a similar mechanism could be present. For instance we find in Richet's 

 (1882) Physiologie des Muscles et des Nerfs three different inhibitory theories 

 for the central nervous system discussed, none of which takes inhibitory 

 nerves for central actions into account. This notwithstanding the fact that 

 Richet is often credited with being the first to have described peripheral 

 inhibition in the crayfish. This credit belongs, however, to Biedermann (1887, 

 1888) who became convinced of it on rather weak evidence, whereas Richet's 

 remark was of the order of a hunch. 



Without committing himself, Foster (1880) came closest to visualizing a 

 theory on the basis of inhibitory fibers in his Text Book of Physiology. He 

 points out that one view on respiratory inhibition ascribes this to the presence 

 of inhibitory fibers in the ascending vagus. About the descending vagus he 

 states "Here again it is usually said that the pneumogastric contains cardio- 

 inhibitory fibres" and notes that in both these cases the examples are of the 

 action on automatically active structures. Elsewhere he states "But we have 

 seen that active nervous centres are subject not only to augmentative, but also 

 to inhibitory influences." "Hence the cardio-inhibitory centre (in the medulla) 

 might itself be inhibited by impulses reaching it from various quarters." "In 

 other words, the beat of the heart might be quickened by lessening of the 

 normal action of its inhibitory centre in the medulla." This to me appears to 

 contain the essential features of the presence of a general system of specific 

 inhibitory fibers. 



Sherrington (1906) was undoubtedly influenced by these views. He starts 

 out by quoting the vagus, the Anodonta preparation of Pavlov (1885), and the 

 crayfish peripheral inhibition. The latter were the first instances of inhibitory 

 action on a non-automatic active structure. But then, rather than accepting 

 inhibitory fibers, Sherrington conceives of specific inhibitory endings, as 

 branches of axons which have also excitatory function. His reasons for this 

 view are varied and rest on such observations as the increased reflex excit- 

 ability after strychnine. Another difficulty he could not solve by purely 

 inhibitory axons was the fact that in rhythmic reflexes, such as the scratch 

 reflex, continuous stimulation of certain sensory fibers evoked both excitation 

 and inhibition. In his later views (Sherrington, 1925) in wliich he arrived on 

 the basis of Loewi's vagus substance at the possible presence of excitatory 

 and inhibitory transmitters, he still believed in the dual action of individual 



neurons. 



A very disturbing set of facts for specific inhibitory fibers had in the mean- 

 time developed out of the observations of Wedensky. This well known 

 inhibitory phenomenon, in which excitatory stimulation itself leads to inhibi- 



