EXCITATION AND INHIBITION 435 



explaining total inhibition, whereas it is an experimental fact that inhibition may 

 be complete. 



The part played by the refractory period is described in the text. Also an 

 explanation is suggested for the results of von Frey on the vasomotor nerves of 

 the submaxillaiy gland. 



It is shown how the theoretical basis of the theories according to which 

 " assimilation " or " anabolism " is associated with inhibition is unsatisfactory, 

 and that, if we look upon cell processes from the dynamic point of view, increase 

 of anabolism seems to necessitate increase of catabolism also, instead of decrease, 

 as such theories of inhibition require. 



There is no satisfactory evidence that the increase of functional capacity, some- 

 times found to be present after inhibition, is actually due to an increased building 

 up by the inhibitory stimuli. On the other hand, the fact that fatigue of inhibition 

 in nerve centres is found to occur does not necessarily exclude an anabolic explana- 

 tion, since the fatigue may be situated in an intermediate excitatory synapse. 



The seat both of excitation and of inhibition in nerve centres is in the synapses, 

 so that fatigue must in all probability be here also. 



There is a fundamental misconception at the basis of the " drainage " theories, 

 namely, that the amount of nerve "energy" present in the neuro-muscular system 

 is a constant, limited quantity. Moreover, the occurrence of inhibition without 

 simultaneous excitation elsewhere is left unexplained by such theories. 



The possibility of productiop of a " block " and its relation to the permeability 

 changes of the membrane is briefly discussed. 



Macdonald's theory of adsorption of ions by colloids is shown to have con- 

 siderable importance as a contribution to the theory of inhibition and excitation. 



Inhibition can be changed into excitation by strychnine and similar drugs, 

 while excitation can be changed into inhibition by chloroform. The most 

 satisfactory explanation seems to be that the actual processes themselves are 

 reversed. The possibility of a similar phenomenon being concerned in the reversal 

 of peripheral action, such as that of the vagus and of the chorda tympani by 

 certain alkaloids, is pointed out. 



The process of excitation in plants, apart from movement, is shown to be 

 essentially similar to that in animals, being independent of visible effects, and 

 accompanied by electrical negativity of the excited protoplasmic structures. 



Conduction of excitation in plants appears to be through protoplasmic 

 continuity of cells, since it can be abolished by local application of anaesthetics. 



The " anti-oxydase " reaction of Czapek, as associated with stimulation in plants, 

 is described. 



LITERATURE 



General. 



Keith Lucas (1912). 



All or-Noihing Principle. 

 Adrian (1913-1914). 



Refractory Period. 



Bramwell and Lucas (1911). 



Nernst Theory. 



A. V. Hill (1910). Keith Lucas (1910). 



Intermediate Substances. 



Sheriington (1906, pp. 83-106, 133-148, 191-199). Macdonald (1905, pp. 331-350). 

 Forbes (1912). 



Excitation in Plants. 



Pringsheim (1912). Burdon-Sanderson (1888). 



Inhibition. 



Langley (1906). Keith Lucas (1906, 1 and 1907, 1). 



