478 THE SENSORIAL FUNCTIONS. 



and frequently by volition ; and also to convey to 

 the muscles of voluntary motion the influence 

 which causes them to contract in obedience to the 

 determinations of the will. The first is termed the 

 ganglionic, and the second the sensorial part of the 

 nervous system. 



Each of these two sets of organs consists of the 

 following four parts, distinguishable by the special 

 offices they perform in their respective system. 

 First, the afferent nerves, composed of fibres of 

 white neurine, extend from the part where the 

 original irritation or impression is made to certain 

 central parts of the nervous system. Secondly, the 

 central organs themselves, in which the afferent 

 nerves terminate, consist of masses of grey neurine, 

 and are now generally regarded as furnishing that 

 peculiar power, whatever be its nature, which 

 effect the operations carried on by the nervous sys- 

 tem. In the case of the reflex functions, this power, 

 as has been already observed, is of a purely physi- 

 cal character, and may exist in organizations where 

 no mental phenomena take place : as is apparently 

 exemplified in some of the simplest forms of living 

 beings ; and as occurs in the cases in which vitality 

 survives for a time the total abolition of sensitive 

 existence, and even in detached portions of the 

 body. But in the case of the sensorial functions, 

 the grey neurine exercises the still higher office of 

 being the primary medium of connexion between 

 the mind and the body ; receiving impressions 

 from the nerves of sensation, renewing and com- 

 bining these impressions, contributing to the ope- 

 rations of the intellect, and lastly, conveying to the 

 nerves of voluntary motion the commands of the 



