cxxxiv NEKVOUS SYSTEM. 



is contained in the proper nervous substance, a portion forming the central part of 

 the nerve-fibres (axis-cylinder) appears in microscopic observations to be solid ; 

 whilst in the surrounding part (medullary sheath) the albuminoid is liquid and in- 

 corporated with fatty matter, also liquid, being probably combined as a colloid with 

 the fat, in the way pointed out by Mr. Graham (see ante, page vii). The fats are 



1. The cerebric acid of Fremy, called cerebrin by Gobley, because he considers it a 

 neutral body, acid only from contamination with phosphoric acid, but containing 

 phosphorus, which also is regarded as an impurity by W. Miiller. 



2. Oleo-phosphoric acid of Fremy, a very unstable compound, held by Gobley to 

 be a mixture of oleic acid and his gl ycero-phosphoric acid, which, it may be remarked, 

 he has found also in the yelk of the egg. 



3. Olein, margarin, and palmitin, with their acids. 



4. Cholesterin although this is no longer considered a true fat, and may, moreover, 

 "be a product of tissue-change. 



The extractive matters probably belong chiefly to the interstitial fluid ; but, how- 

 ever this may be, they may be held to represent the products of decomposition of 

 the nervous substance. The following have been recognised : 



1. Lactic, formic, acetic, and (traces of) uric acid. 



2. Inosit. 



3. Kreatin. 



4. Hypoxanthin (or sarkin). 



5. Leucin(in the ox). 



In regard to free acid, Funke has found the same law to prevail in nerve as in 

 muscle namely, that the substance of nerves in the living but quiescent state is 

 neutral, but becomes acid after death or prolonged excitement. The saline or inor- 

 ganic matters found by incineration are phosphoric acid, phosphates of alkalies, 

 which, as in muscle, largely predominate over other salts, potash, as a base, largely 

 exceeding soda ; earthy phosphates, in smaller proportion, magnesia prevailing over 

 lime ; phosphate of iron ; chloride of sodium, sulphate of potash, and a trace of 

 silica. From fresh brain-substance Breed obtained - 027 per cent, of ashes, which 

 per 100 parts yielded 55'24 phosphate of potash, 22 93 phosphate of soda, V23 phos- 

 phate of iron, r<32 phosphate of lime, 3*4 phosphate of magnesia, 474 chloride of 

 sodium, T64 sulphate of potash (the sulphuric acid doubtless from combustion of 

 principles containing sulphur), 9'15 free phosphoric acid (from combustion of phos- 

 phorus), and 0*42 silicic acid. 



The white substance contains nearly 75 per cent, of water; the grey about 85; 

 the proportion of water is less in the spinal cord, and still less in the nerves. The 

 fat amounts in the grey matter to nearly 5 and in the white to nearly 15 per cent.; 

 in the nerves the proportion fluctuates largely. It is worthy of note that the brain, 

 during embryo and infantile life, contains much less fat and more water ; moreover, 

 the grey and the white matter do not present the same differences as in after life in 

 the proportions of water and fat which they respectively contain. The brain of 

 embryos of from ten to twenty-two weeks has been found to yield only from 0'99 to 

 1-5 per cent of fat ; that of the full grown foetus from 3 to 4 per cent. The water in 

 the foetal brain at birth is about 85 per cent., both in the white and the grey sub- 

 stance. 



STRUCTURAL ELEMENTS. 



When subjected to the microscope, the nervous substance is seen to con- 

 sist of two different structural elementa, viz., fibres and cells. The fibres 

 are found universally in the nervous cor<ls, and they also constitute the 

 greater part of the nervous centres : the cells on the other hand are con- 

 fined in a great measure to the cerebro-spinal centre and the ganglia, and do 

 not exist generally in the nerves properly so called, although they have been 

 found at the terminations of some of the nerves of special sense, and also 

 interposed here and there among the fibres of particular nerves ; they are 

 contained in the grey portion of the brain, spinal cord, and ganglia, which 

 grey substance is in fact made up of these cells intermixed in many parts 

 with fibres, and with a variable quantity of supporting connective substance. 



