Physiology of Central Nervous System 75 



change of condition whicli may he produced wlirii onr variahh* 

 is changed; it is not surprising tliat tlicre should Im- sudden 

 changes in the ontogenetic and phylogrnetic development 

 of organisms when then* are so many variaMes 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 (hscovery to he made in the 

 field of brain physiology and psycholog>'. But at the same 

 time it is evident that this mechanism cannot be unrav<'led 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 chang«*s occurring 

 in colloidal substances. The question is. Which peculiarities 

 of the colloidal substances can make the phenom<'non of asso- 

 ciative memory possible? For the solution of this prol^lem 

 the experience of phj'sical chemistry and of the i)hysi()log>- of 

 the protoplasm must be combined. From the sam<' sourc(»s 

 we must expect the solution of the other fundamental problems 

 of brain physiology, namely, the process of conduction of 

 stimuli. 



