TISSUES OF THE BODY. 339 



occur in nervous tissue, apart from a small amount of it in a soluble form, 

 is still uncertain. Quantitively it is impossible to analyse them on 

 account of being obliged to include the primitive sheath, and other tissue 

 elements. The amount, besides, of residue insoluble in ether varies 

 considerably, from 9 to 14 per cent. 



As soluble in ether, we obtain further the so-called cerebral substances 

 lecithin and cerebrin ( 20), and likewise cholesfearin in considerable 

 quantity ( 21). The amount of these matters, further, has been found 

 to be far greater in the white substance of the brain than in the grey, 

 and they may, therefore, be regarded as essentially constituents of the 

 nervous medulla, although we do not possess any satisfactory explana- 

 tion of the manner in which they occur here being insoluble in water. 



From the fact that lecithin (which exists in great quantity in the brain), 

 yields, besides neurin ( 33), and glycerophosphoric acid ( 16), palmi- 

 tinic and oleic acid also, we may infer that the fatty acids and fats, upon 

 which such stress used formerly to be laid, were possibly only products 

 of the decomposition of the former. 



Clwlestearin, which occurs in cerebral tissue in large quantities (amount- 

 ing, according to Von Bibra, to a third of the matters soluble in ether), has 

 the nature likewise of a decomposition product. 



Turning now to the quantity of these matters soluble in ether, we find 

 their proportion in the grey substance, in which much water is contained, 

 to be 5-7 per cent. ; in the white tissue, which is poorer in the latter, on 

 the other hand, it is 15-17 per cent., and rises still higher in the spinal 

 cord. Considerable difference may be observed, also, between the various 

 parts of the same brain. In the infant the amount of these matters is 

 very small, there being, besides, no difference in this respect between the 

 white and grey tissue. In the foetus they are present in still smaller 

 quantity. 



Among the products of transformative processes going on in nervous 

 tissue, may be reckoned formic and lactic acid (found in the brain), and 

 possibly also acetic acid, also inosit, Jcreatin, leucin (in the ox), xantliin 

 and hypoxanthin (Scherer), urea (in the dog), and uric acid. 



The ash of cerebral substance amounts, according to Breed, to 0*027 

 per cent, of the fresh tissue. In a hundred parts of the former he found : 



Free phosphoric acid, . . . . . 9 '15 



Phosphate of potassium, . . . . . 55 '24 



of sodium, 22 -93 



of iron, 1-23 



of calcium, 1'62 



of magnesium, . . . . 3 '40 



Chloride of sodium, ..... 4*74 



Sulphate of potassium, . . . . . 1'64 



Silica, 0-42 



The preponderance of potash and magnesia over soda and lime recalls 

 to mind the state of things in muscle. 



191. 



Turning now to the application to neural physiology of the points 

 regarding the structure of the nervous apparatus, which have just been 

 described, w see in the first place, in the two kinds of structural elements, 

 a contrast between merely conducting fibres and cells which are endowed 



