CH. XVI.] THE EVOLUTION OF MIND. 149 



and "both are at the minimum, a great many discharges are 

 necessary for the achievement of any permanent nutritive 

 change : hence learning is slow and difficult, and memory is 

 feeble. And hence — what is most significant of all — the 

 old man does not remember recent events, while he re- 

 members very well what happened in his youth, when his 

 rate of nutrition was rapid. These and countless similar 

 facts show us that a state of consciousness and a nutritive 

 change in the cej)halic ganglia are correlated like the sub- 

 jective and objective faces of the same thing. And thus are 

 explained the many facts which in the seventh chapter were 

 brought forward in illustration of the transformations of vital 

 energy, — such as the facts that consciousness ceases the 

 instant the carbonic acid in the blood has attained a certain 

 ratio to the oxygen ; that much thinking entails a great ex- 

 cretion of alkaline phosphates ; and that prolonged mental 

 exertion is followed by a bodily fatigue and a keen appetite 

 not essentially different from the fatigue and hunger which 

 follow muscular exercise. 



Eegardiiig it now as provisionally established that an 

 association of ideas is dependent upon the formation of a 

 transit-line between two nerve-cells, and that the more often 

 the fibrous path is traversed the more indissoluble will be 

 the association, let us proceed briefly to apply this doctrine 

 to the explanation of sundry psychical phenomena. Now as 

 we begin to examine the simplest psychical phenomena — 

 those of reflex action and instinct — we are met by the seem- 

 ing difficulty that indissolnbly connected psychical states 

 occur where the corresponding objective relation has never 

 been repeated within the experience of the individual. In- 

 stinctive adjustments of inner to outer relations are appa- 

 veutly made without any help from experience. Motlis and 

 butterflies take to wing immediately on emerging from the 

 envelope of the chrysalis ; " a fly-catcher, immediately after 

 its exit irom the egg, has been known lo peck at and capture 



