14 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



mechanical arrangements for associative memory, 

 and therefore for metaphysical consciousness, is not 

 stranger than the fact that only certain animals 

 possess the mechanical arrangements for uniting the 

 rays from a luminous point in one point on the 

 retina. The liquefaction of gases is an example of a 

 sudden change of condition which may be produced 

 when one variable is changed ; it is not surprising 

 that there should be sudden changes in the onto- 

 genetic 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 unravelling of the 

 mechanism of associative memory is the great dis- 

 covery to be made in the field of brain-physiology 

 and psychology. But at the same time it is evident 

 that this mechanism cannot be unravelled by histo- 

 logical 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 sub- 

 stances can make the phenomenon of associative 

 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-physio- 

 logy, namely, the process of conduction of stimuli. 



