CHARACTERISTICS OF NERVOUS TISSUES. 775 



in solution when a 10 per cent, salt solution of brain is boiled; it may 

 be precipitated after filtering by the addition of acetic acid. 



Nuclein, also, is found, especially in the gray matter; while in the 

 sheath of nerve-fibres after the removal of the fatty matters by boiling 

 alcohol and ether a nitrogenous body is found which is termed neuro- 

 keratin, and which in its composition appears closety related to keratin 

 and is especially characterized by the sulphur (2.93 per cent.) which it 

 contains. 



Neurokeratin is not affected in gastric or pancreatic digestion ; it 

 swells in caustic potash and strong sulphuric acid, but only dissolves in 

 these liquids when boiled. 



Gelatiu is likewise found in nerves, but is evidently derived simply 

 from the connective tissue of their sheaths. 



Fats are present in large amounts, especially in the white matter and 

 in the white substance of Schwann, which appears to be almost solely of 

 a fatty nature. 



The specific constituents of the brain and nerves are of a highly 

 complex character and may be divided into two groups those which 

 contain phosphorus in combination and those which are free from phos- 

 phorus. As an example of the first of these, protagon may be mentioned, 

 which, discovered by Liebreich, has been regarded by many chemists, 

 not as a distinct body, but as a mixture of lecithin, a phosphorized fat, 

 with cerebrin, a nitrogenous, non-phosphorized body. Experiments by 

 Gamgee have, however, apparently proven that protagon is a definite 

 chemical body, soluble in cold alcohol with difficulty, readily soluble in 

 warm alcohol and ether. To this substance Gamgee attributes the em- 

 pirical formula C 160 H 308 X 5 P035. It forms a clear solution with glacial 

 acetic acid. 



Cerebrin is. an example of the special brain-constituents which are 

 free from phosphorus; it appears, however, that cerebrin, as described 

 by Mu'ller, is not a distinct body, but a mixture of cerebrin, homocere- 

 brin, and encephalin. 



The entire subject of the organic constituents of the nervous sj'stem 

 needs to be re-examined, since on any matter where such diametrically 

 opposite opinions are held the error on both sides must be considerable. 



Like the muscular tissue, nervous substance when passive has a 

 neutral or even faintly alkaline reaction ; after prolonged stimulation or 

 functional activit} T , produced in any wa} T , the reaction becomes acid. 



After death the reaction likewise becomes acid and the nerves become 

 more solid, thus resembling the similar changes which occur in muscle, 

 and, although not thoroughly investigated, in all probability are due to a 

 similar process. 



Nerve-fibres are free from elasticit}', and if divided do not retract : 



