Physiology of Central Nervous System 75 



change of condition which may be produced when one variable 

 is changed; it is not surprising that there should be sudden 

 changes in the ontogenetic and phylogenetic development 

 of organisms when there are so many variables subject to 

 change, and when we consider that colloids easily change their 

 state of matter. 



It becomes evident that the unraveling of the mechanism 

 of associative memory is the great discovery to be made in the 

 field of brain physiology and psychology. But at the same 

 time it is evident that this mechanism cannot be unraveled by 

 histological methods, or by operations on the brain, or by 

 measuring reaction times. We have to remember that all life 

 phenomena are ultimately due to motions or changes occurring 

 in colloidal substances. The question is, Which peculiarities 

 of the colloidal substances can make the phenomenon of asso- 

 ciative memory possible? For the solution of this problem 

 the experience of physical chemistry and of the physiology of 

 the protoplasm must be combined. From the same sources 

 we must expect the solution of the other fundamental problems 

 of brain physiology, namely, the process of conduction of 

 stimuli. 



