Section III. 

 I/ETHODS OP Investigation. 



The technique employed in the course of this research has 

 covered a wide range. In fact, every process holding any promise 

 of value has been given a careful trial. It seems desirable to 

 describe here, however, only those aiethods which have contrib- 

 uted most largely to the final results. 



1. Chrome-Si Iver Impregnation . 

 The production of a chrome-silver deposit in nervous ele- 

 ments is far more than a simple chemicsl reaction between the 

 potassiun, bichromate and the silver nitrate employed. There 

 is to be added as a prime factor, the chemistry of the nervous 

 tissues themselves. The substances present ir the nervous ele- 

 ments enter into the reaction to such a degree that the results 

 are either positive or negative according to the character of 

 those substances. In the economy of the animal, serving both 

 as the basis for nervous activity and produced as the result 

 of it, there is a constant round of metabolic change altering 



the chemical composition of the nervous tissues. In my work 



(15) 



