CHEMICAL COMPOSITION. cxxxiii 



operating without our consciousness and without the intervention of the 

 will.* 



The nerves are divided into the cerebro-spinal, and the sympathetic or 

 ganglionic nerves. The former are distributed principally to the skin, the 

 organs of the senses, and other parts endowed with manifest sensibility, and 

 to muscles placed more or less under the control of the will. They are 

 attached in pairs to the cerebro-spinal axis, and like the parts which they 

 supply are, with few exceptions, remarkably symmetrical on the two sides of 

 the body. The sympathetic or ganglionic nerves, on the other hand, are 

 destined chiefly for the viscera and blood-vessels, of which the motions are 

 involuntary, and the natural sensibility is obtuse. They differ also from the 

 cerebro-spinal nerves in having generally a greyish or reddish colour, in 

 their less symmetrical arrangement, and especially in the circumstance that 

 the ganglia connected with them are much more numerous and more gene- 

 rally distributed. Branches of communication pass from the spinal and 

 several of the cerebral nerves at a short distance from their roots, to join the 

 sympathetic, and in these communications the two systems of nerves mutually 

 give and receive nervous fibres ; so that parts supplied by the sympathetic 

 may be also in nervous connection with the cerebro-spinal centre. 



The nervous system is made up of a substance proper and peculiar to it, 

 with inclosing membranes, nutrient blood-vessels, and supporting connective 

 tissue. The nervous substance has been long distinguished into two kinds, 

 obviously differing from each other in colour, and therefore named the white, 

 and the grey or cineritious. 



CHEMICAL COMPOSITION. 



The information we possess respecting the chemical composition of nervous 

 matter is for the most part founded on analyses of portions of the brain and 

 spinal cord ; but the substance contained in the nerves, which is continuous 

 with that of the brain and cord, and similar in physical characters, appears 

 also, as far as it has been examined, to be of the same general chemical con- 

 stitution. No very careful comparative analysis has yet been made of the 

 grey and white matter, to say nothing of the different structural elements of 

 the nervous substance ; and indeed it must be remembered, that, in portions 

 of brain subjected to chemical examination, capillary blood-vessels, connec- 

 tive and perhaps other accessory tissues, as well as interstitial fluid, are 

 mixed up in greater or less quantity with the true nervous matter, and must 

 so far affect the result. 



The nervous matter may be said to consist of an albuminoid body, in part 

 liquid, with fatty principles, extractive matters, salts, and much water. The 

 water, which forms from three-fourths to four-fifths or more of the whole 

 cerebral substance, may be removed by immersion in alcohol and evapora- 

 tion. When the solid matter which remains after removal of the water is 

 treated with ether and hot alcohol, the fatty compounds are extracted from 

 it by these menstrua, and there remains a mixture of coagulated albuminous 

 matter and salts, with a small remnant due to accessory tissues, chiefly vessels. 



The albuminoid constituent is not sufficiently known to be characterised specifically. 

 It no doubt belongs, in some small proportion, to the interstitial fluid. Of that which 



* From the researches of Dr. Augustus Waller it appears probable that ganglions 

 exert some influence over the nutrition of the nerve-fibres connected with them, and 

 serve to maintain the structural integrity of these fibres ; for it has been found that, when 

 a ganglionic nerve is cut across in a living animal, the part beyond the section after a 

 time becomes atrophied, while the part connected with the ganglion retains its integrity. 



Tc 



