176 



PHYSIOLOGY OF NERVE 



[CII. XV. 



amount (83 per cent. ) in grey matter than in white matter (70 per cent. ) ; in early 

 than in adult life ; in the brain than in the spinal cord ; in the spinal cord than in 

 nerves. 



One should next note the high percentage of proteid. In grey matter, where 

 the cells are prominent structures, this is most marked, and of the solids, proteid 

 material here comprises more than half of the total. The following are some of my 

 analyses which give the mean of a number of observations on the nervous tissues 

 of human beings, monkeys, dogs, and cats : 



The most abundant proteid is nucleo-proteid ; there is also a certain amount of 

 globulin, which, like the paramyosinogen of muscle, is coagulated by heat at the low 

 temperature of 47 C. A certain small amount of neurokeratin (especially abundant 

 in white matter) is included in the above table with the proteids. The granules in 

 nerve cells (Nissl's bodies), which stain readily with methylene blue, are nucleo- 

 proteid in nature. The next most abundant substances are of a fatty nature ; the 

 most prominent of these is the phosphor ised fat called lecithin. In the nervous 

 tissues some of the lecithin is combined with cerebrin to form a complex substance 

 called protayon, which crystallises out on cooling a hot alcoholic extract of brain or 

 other nervous structures. Cerebrin is a term which probably includes several sub- 

 stances, which are nitrogenous glucosides ; they yield on hydrolysis the sugar called 

 galactose. They are sometimes called cerebrosides. Kephalin is another phos- 

 phorised fat which is present. The crystalline monatomic alcohol cholesterin is also 

 a fairly abundant constituent of nervous structures, especially of the white substance 

 of Schwann. Finally, there are smaller quantities of other extractives and a small 

 proportion of mineral salts (about 1 per cent, of the solids). 



In connection with the substances just enumerated, it is necessary to enter a 

 little more fully into the composition of lecithin. An ordinary fat contains the 

 elements carbon, hydrogen, and oxygen, and when it takes up water it is split or 

 hydrolysed into its constituent parts, glycerin and fatty acid. 



Fat + water. 



I 



Glycerin. 



Fatty acid. 



Lecithin (C 4 . 2 H 84 NPO 9 ) contains not only carbon, hydrogen, and oxygen, but 

 nitrogen and phosphorus as well. When it is hydrolysed, it yields not only glycerin 

 and a fatty acid, but also phosphoric acid, and a nitrogenous base termed choline. 



Lecithin + water. 



I 



Glycerin. 



Fatty acid. 



Phosphoric acid. 



Choline. 



