100 SUPER-ORGANIC EVOLUTION 



lively, Cajal thus sums up the conditions which 

 chiefly, or more or less exclusively, influence mental 

 phenomena : 



" Firstly, the number of nerve-cells of the cortex. 



" Secondly, the variable development of the 

 collateral and terminable protoplasmic expansions 

 of the cylindric axes. 



" Thirdly, the correlative proportions of the 

 corpuscules of association in front of the sensitive, 

 sensory, central, and psychomotor ones. 



"Fourthly, the way in which the medullisation 

 of the nervous fibres is shared, since, the greater 

 the covering of the mielina, the better the isolation 

 of the currents. 



" Fifthly, the relative abundance of interstitial 

 cement, which probably is intended to impede the 

 diffusion of the nerve-movement. 



" Sixthly, the variable number of neuroglic cells, 

 whose office appears to be to separate the nerve- 

 fibres, to avoid contact and filtration of currents. 



" Seventhly, the state of the reticulum or inter- 

 cellular woof (still very little known). 



" Eighthly, the existence of perturbations or 

 modifications more or less lasting in the chemical 

 combination of the cells and interstitial cement. 



"By this we mean only the anatomical condi- 

 tions of the grey substance; but it is clear that 

 they may also influence the absolute or relative 



