132 Dr. Frederick Walker Mott [April 21, 



come into play to join up the visual area with the centre of movement 

 of the hand, that is to say, that impulses must pass from the back to 

 the middle of the brain. These conscious motor responses to sensory 

 impressions are truly psychical reflexes, because the nervous current 

 is bent back from the sensory ingoing system down along the motor 

 system to the muscles. 



I have told you there is reason to believe that every neurone 

 is an independent unit, and although its processes appear to enter 

 into an inextricable network, yet there is really no continuity of 

 structure. By inference we should believe this view to be correct, 

 because if the whole of the nervous elements were connected together, 

 diffusion of the nervous current through the whole substance of the 

 brain would occur, and instead of orderly sequence, only confusion 

 could arise in response to an external stimulus. If the neurones then 

 are separate living units, can they by biochemical or biophysical pro- 

 cesses promote or retard the transmission of currents along systems 

 or between clusters, groups and communities ? The method of contact 

 between two neurones is always by the terminal arborisation of the 

 nerve fibre process of one with the branching protoplasmic processes 

 of another. Movements in the nerve cell of a minute aquatic animal 

 having been observed under the microscope, it was conceived that 

 the terminal twigs of the nerve fibre process might elongate, and 

 come in better contact therefore with the protoplasmic processes of 

 the next neurone of the series ; and it has also been thought that sleep 

 and unconsciousness from anaesthetics and narcotics, also trance and 

 the hypnotic state, might be due to retraction of the terminal twigs 

 of the sensory neurones on the surface of the brain so that contact 

 is broken, and the transmission of nervous currents consequently 

 interrupted. 



It has been attempted to found a theory of retraction of the 

 terminal buds or points of contact of the branching processes of the 

 dendrons, by fixing in various fluids small pieces of the brain of 

 animals which have been anaasthetised with chloroform and other 

 anaesthetics and narcotics, and compariug the appearances presented 

 by the dendrons with those presented by the brain of an animal killed 

 suddenly. One set of observers finds retraction during narcosis, with 

 the appearance of little moniliform swellings on the processes and 

 disappearance of the gemmules. Another set finds no retraction of 

 the gemmules, but retraction they say occurs when the brain is in 

 activity ; thus the facts are entirely opposed to one another. My 

 observations, also those of my assistant Dr. Wright, who has given 

 special attention to this subject, are opposed to the facts stated by 

 the first set of observers (Figs. 2 and 9). 



The whole difficulty lies in the fact that we are looking not at 

 living matter but dead matter ; still the theory of association and 

 dissociation of groups or systems of neurones subserving special 

 functions is an attractive theory for explaining the problems of 



