MECHANICAL PROPERTIES OF NERVES. 627 



Neurokeratin, a phosphorus-free substance rich in sulphur and closely 

 related to keratin, occurs in the horny sheaths of the nerve-fibers, remain- 

 ing after artificial digestion of the gray nervous substance by trypsin; 

 treatment of the resulting product with potassium hydroxid yields pure 

 neurokeratin. The material of the sheath of Schwann closely resembles 

 elastin, although it is more readily soluble in alkalies. The connective 

 tissue of the nerves yields gelatin. 



Fats and fat-like substances soluble in ether occur principally in the 

 white matter as follows: 



(a) Liebreich's protagon, which resembles cerebrin, is readily de- 

 composed, contains nitrogen and phosphorus, doubtfully sulphur, is the 

 principal constituent of the brain-mass, but is wanting in the ganglion- 

 cells, as well as in their decomposition-products. 



It can be extracted from the white central nerve-mass by treatment with 

 85 per cent, alcohol at 45 C. It is readily soluble in ether, glacial acetic acid, 

 and benzol, scarcely soluble in alcohol, and crystallizes in plates. It swells 

 in water and becomes opalescent. When heated to 50, the glucosid-like, phos- 

 phorus-free body, cerebrin, is separated. Boiled with baryta it yields the de- 

 composition-products of lecithin. Protagon was considered by Diakonow and 

 Hoppe-Seyler as a mixture of lecithin and cerebrin. 



(6) Cerebrin occurs as a decomposition-product of protagon. 



It is a white powder, consisting of spherical, transparent, smooth granules 

 containing nitrogen, but free from phosphorus, soluble in hot alcohol, chloroform, 

 and benzol, insoluble in ether or water. Boiled with dilute sulphuric acid it 

 is decomposed into galactose and a fat. Parkus has separated from cerebrin 

 homocerebrin (kerasin) , a homologous readily soluble body, crystallizing in 

 needles, and encephalin, which swells up in hot water like starch and contains 

 an additional molecule of water. 



(c) Lecithin is chemically combined in protagon. In addition there 

 are present decomposition-products of lecithin, such as glycerophosphoric 

 acid, oleophosphoric acid. 



Lecithin is an ether-like combination of neurin in which the latter takes the place 

 of the alcohol. It is of waxy consistence and it swells in water in myelin-f orms ; 

 it is soluble in alcohol or ether. Neurin, C 5 H 15 NO 2 , is a strongly alkaline, colorless 

 fluid, forming crystalline salts with acids. It can be produced synthetically 

 from glycol and trymethylamin ; it is soluble in water and in alcohol. Neurin 

 results by reduction from cholin; muscarin results by oxidation from cholin. 

 Cholin is non-toxic, while neurin and muscarin are toxic. Cephalin closely re- 

 sembles lecithin; it is precipitable from an ethereal solution by alcohol and is 

 stained black by osmium. 



(d) Cholesterin occurs partly free and partly in combination in the 

 ganglia and in larger quantities in the white matter. 



Whether neutral fat or fatty acids occur has not been positively de- 

 termined. 



3. The following products of retrogressive tissue-metamorphosis can 

 be extracted by water: xanthin, guanin, and hypoxanthin, (?) adenin, 

 kreatin, urea (in larger amount in case of retention of urine), (?) uric 

 acid, jecorin, neuridin, a diamin occurring in connection with putrefac- 

 tion. Further, W. Miiller has found formic and acetic acids, taurin, 

 much inosite, and in cattle leucin; v. Bibra, fermentation lactic acid, 

 and Jaffe, a starch-like substance in human brains. 



Nervous tissue in a state of rest has a neutral or slightly alkaline 

 reaction, while when active and also when dead the reaction is acid. 



The cerebral cortex in the fresh state yields an alkaline reaction, which 



