Neural Integration 167 



haphazardness disappears. Nerve conduction in a nerve 

 trunk as an isolated phenomenon has neither existence nor 

 meaning for the actual organism. The conducting element 

 par excellence of the real unit of nerve organization is 

 differentiated with reference to the other elements of that 

 unit, and normally acts only in such relation. The circum- 

 stance that this element is found to have the ability to act 

 somewhat differently under different but abnormal rela- 

 tions signifies little or nothing, so far as one can see, for 

 the normal workings of the nervous system. What it does 

 show is something of the diversity and plasticity of the 

 organism because of its latent ability to act otherwise than 

 in nature it does act when conditions are imposed upon it 

 which are wholly new to it. 



Although the explanation of this irreversibility of direc- 

 tion appears not to be known with certainty, the suggestion 

 that it may be connected with a difference in permeability 

 of the synaptic membrane between cells of the reflex-arc to 

 certain ions, depending upon which side of the membrane is 

 presented to these ions, is plausible and indicates the re- 

 sourcefulness, as one might say, of structural and functional 

 method by which the organization of the living being is ac- 

 complished. Should this suggestion prove to be correct, 

 the question would arise, how comes it that the synaptic 

 membrane is thus differential in its action? And no ade- 

 quate answer would be forthcoming that did not take cogni- 

 zance of the fact that the membrane assumed this differential 

 mode of acting as part and parcel of the differentiation and 

 integration as the reflex-arc as a whole. 



Sherrington deals with a whole series of other differences 

 between nerve trunk conduction and reflex-arc conduction, 

 such as the phenomena of summation of stimuli, that is, 

 the adding up of excitations too slight taken singly to pro- 

 duce reaction, until the aggregate brings response. Such 

 are rhythmic activity in response to stimuli which are not 



