en. xvi.] THE EVOLUTION OF MIND. 141 



nutrition is notably retarded, as by the anaemia and feeble 

 circulation of disease or old age, new associations of ideas 

 become difficult or even impossible. 



To sum up this whole preliminary argument: the 

 cerebrum and cerebellum are organs whose function is 

 ideation or the generation of ideal feelings and thoughts. 

 They are organs made up of a tissue in which chemical 

 changes occur with unparalleled rapidity. We cannot see 

 these changes go on, but we can equally well infer their 

 general character when we have examined the chemical 

 properties and molecular structure of the tissue in which 

 they occur. Microscopic and chemical examination of this 

 tissue shows that these chemical changes must consist in a 

 perpetual transfer of energy from one cell to another along 

 transit-lines composed of nerve-threads. Bear in mind that 

 the cell does not average more than one ten- thousandth of 

 an inch in diameter, and that the quantity of matter con 

 tained in a transit-line is almost infinitely small. Now since 

 the cerebrum and cerebellum are, subjectively speaking, 

 places where ideation is continually going on ; and since they 

 are, objectively speaking, places where nerve-cells are con 

 tinually sending undulations back and forth along transit- 

 lines ; the inference seems forced upon us, that the transfer 

 of an undulation from one cell to another is the objective 

 accompaniment of each subjective unit of feeling of which 

 thoughts and emotions are made up. And if this be so, it 

 becomes a mere truism to say that the formation of a new 

 association involves the establishment of a new transit-line, 

 w set of transit-lines, while the revival of an old association 

 involves merely the recurrence of motion along old transit- 

 lines. That this is merely a hypothesis, I readily grant. 

 Nevertheless it is a verifiable hypothesis ; it is in harmony 

 with all that we know of nerve -action ; and it may be held 

 provisionally until some better one is propounded. When 

 we proceed to see how many phenomena it explains, we shall 



