CHAP. X.] THE NERVOUS TISSUES. 423 



SECT. 2. THE PROTEIDS FOUND IN THE NERVOUS TISSUES. 



More than one-half of the solids contained in the grey matter, and 

 about one-fourth of the solids of the white matter of the nerve-centres, 

 consist of proteid substances, and yet our knowledge of these is but 

 scanty. 



Amongst these proteid bodies are to be mentioned, (1) a proteid 

 substance which is soluble in water and is coagulated at 75 C. ; this 

 probably is derived from the grey matter ; (2) a globulin-like body 

 which is dissolved by a 10 per cent, solution of sodium chloride and is 

 precipitated from it when the same salt is added to saturation ; and 

 (3) an alkaline albuminate, which remains in solution when a 10 per 

 cent, salt solution of brain is boiled; in the solution filtered from 

 coagulated proteids, acetic acid produces an abundant precipitate 1 . 



SECT. 3. NEUROKERATIN AND NUCLEIN. 



NeuroJceratin. 



If medullated nerve -fibres are treated with boiling alcohol and 

 ether, so as to extract the fatty matters of the medullary sheath, there 

 is left in its place an irregular framework which is highly refractile, 

 and which is scarcely affected by digestion with trypsin or pepsin. 

 This refractory substance swells when placed in concentrated sulphuric 

 acid and in solution of caustic potash, but only dissolves in these 

 liquids when boiled. 



The substance resembles, indeed, the horny matter of epidermis in 

 its power of resisting powerful chemical agents, and has been called 

 by Kiihne and Ewald 2 , who have studied its properties, Neuro- 

 keratin. 



The substance is found not only in medullated nerve-fibres, but in 

 the grey matter of the nerve-centres and in the retina ; it appears not 

 to be present in non-medullated nerve-fibres. 



Ox's brain is washed in water, finely divided, digested for a 



Mode of se- j on g time in cold alcohol, again pounded, pressed, treated 



rokeritf/ 6 with alcoho1 - Then full 7 extracted with ether ; dried in the air, 



and powdered. The dry powder is shaken through hair 



sieves and boiled with alcohol, until this liquid dissolves no more cerebrin. 



The residue is boiled with water, pressed and digested with pepsin and the 



insoluble residue washed ; it is then digested for 24 hours in a weak 



solution of trypsin containing salicylic acid, and afterwards it is digested at 



1 The most recent observations on the proteids of the brain are contained in a paper 

 by Petrowsky entitled " Zusammensetzung der grauen und der weissen Substanz des 

 Gehirnes." Pfl tiger's Archiv, Vol. vn. p. 367. 



2 A. Ewald und W. Kiihne, " Ueber einen neuen Bestandtheil des Nervensystems" 

 (Neurokeratin). Verhand. d. naturh. med. Vereins zu Heidelberg, Vol. i. Heft 5. 



