CIT. XIV.] 



CHEMISTRY OF NERVE 



165 



production of a chemical material which plays the part of a stimulus, 

 and if it is rendered inactive by the production of chemical changes 

 of an opposite kind, we really only throw the difficulty further back ; 

 for we do not know how it is that the nervous impulses produce 

 these chemical effects on the receptive substance or substances. 



Chemistry of Nervous Tissues. 



Fresh nervous tissue is alkaline to litmus, but like most other 

 living structures, it turns acid after death; this change is more 

 rapid in grey than in white matter. The acidity is due to sarco- 

 lactic acid. 



Nervous tissues contain a high percentage of water ; the following 

 table gives the mean of a large number of analyses I have made: 



Proteins. The above table shows also the high percentage of 

 protein which is present. In grey matter where the cells are 

 prominent structures this is most marked, protein here comprising 

 more than half of the solids present. 



The most abundant protein is nucleo-protein, and micro-chemical 

 observations have shown that the granules in nerve-cells (Nissl's 

 granules) which stain readily with methylene blue and other basic 

 dyes are nucleo-protein in nature. There is also a certain amount 

 of globulin, which, like the paramyosinogen of muscle, is coagulated 

 by heat at a low temperature (in mammals 47 C). Neurokeratin, 

 which is especially abundant in white matter, is also present. 



A nerve, or a strip of the central nervous system, shortens when 

 it is heated; this "heat contraction" occurs in a series of steps, 

 which, as in the case of muscle, take place at the coagulation 

 temperatures of the proteins present. The first step in the shorten- 

 ing occurs in the frog at about 40, in the mammal at about 47, and 

 in the bird at about 52 C. The nerve is killed at the same 

 temperatures. 



Lipoids. These are also abundant constituents of nervous tissue ; 



