TiS AN INTRODUCTION TO SCIENCE 



forces produce when, on being passed through to his 

 muscles, they upset the unstable molecules of those organs. 

 The case is recorded of a man in whom disease of the 

 nervous system had advanced until he was blind with one 

 eye, deaf with both ears, and had lost cutaneous sensation. 

 One eye alone of all his sense-organs was left to give him 

 information of the outer world. When this was closed he 

 went to sleep. There can be little doubt, as Sir Michael 

 Foster observes, that if the brain were cut off from all 

 external stimuli, "volitional and other psychical processes 

 would soon come to a standstill, and consciousness vanish." 

 If, therefore, we look at the nervous system as a whole from 

 a purely physiological standpoint we have already touched 

 upon the problem of consciousness we find it a mere trans- 

 mitter of impulses. How much more should we expect to 

 find this true of each separate nerve-cell and its conduct- 

 ing fibre? 



We will try to give a very brief historical sketch of the 

 problem, which for clearness we will define as follows : 

 Does the nervous system control the tissues in any sense 

 other than that of transmitting to them intact and unchanged 

 the impulses which originate in its terminations either on 

 the surface of the body or within the body ? And since, as 

 we shall presently find, the only element of nervous tissue 

 which can be imagined as manipulating messages in the 

 course of their transmission is the nerve- cell, the question 

 may be reduced to this simple form Has the nerve-cell any 

 functions beyond that of providing for the nutrition of the 

 fibre which grows out of it ? 



The first great step in nerve physiology was taken by Sir 

 Charles Bell, when (in 1811) he proved that of the two^ roots 

 by which every spinal nerve is attached to the spinal cord, 

 the one, the posterior, conducts sensory impulses toward 

 the centre ; the other, the anterior, conducts motor impulses 

 towards the periphery. 



Bell's discoveries suggested various investigations to 



