PROFESSOR VJRCHOW AND EVOLUTION. 629 



That "matter is not itself alive" Professor Knight 

 seems to regard as an axiomatic truth. Let us place in 

 contrast with this the notion entertained by the philosopher 

 Ueberweg, one of the subtlest heads that Germany has 

 produced. " What occurs in the brain," says Ueberweg, 

 " would, in my opinion, not be possible, if the process 

 which here appears in its greatest concentration did not 

 obtain generally, only in a vastly diminished degree. Take 

 a pair of mice and a cask of flour. By copious nourish- 

 ment the animals increase and multiply, and in the same 

 proportion sensations and feelings augment. The quantity 

 of these latter possessed by the first pair, is not simply 

 diffused among their descendants, for in that case the last 

 in ust feel more feebly than the first. The sensations and 

 feelings must necessarily be referred back to the flour, 

 where they exist, weak and pale it is true, and not concen- 

 trated as they are in the brain."* We may not be able to 

 taste or smell alcohol in a tub of fermented cherries, but 

 by distillation we obtain from them concentrated Kirsch- 

 wasser. Hence Ueberweg's comparison of the brain to a 

 still, which concentrates the sensation and feeling, pre- 

 existing, but diluted in the food. 



" Definitions," says Mr. Holyoake,f " grow as the horizon 

 of experience expands. They are not inventions, but 

 descriptions of the state of a question. No man sees alt 

 through a discovery at once." Thus Descartes' notion of 

 matter, and his explanation of motion, would be put aside 

 as trivial by a physiologist or a crystallographer of the 

 present day. They are not descriptions of the state of the 

 question. And yet a desire sometimes shows itself in dis- 

 tinguished quarters to bind us down to conceptions which 

 passed muster in the infancy of knowledge, but which are 

 wholly incompatible with our present enlightenment. Mr. 

 Martineau, I think, errs when he seeks to hold me to views 

 enunciated by " Democritus and the mathematicians." 

 That definitions should change as knowledge advances is in 

 accordance both with sound sense and scientific practice. 

 When, for example, the undulatory theory was started, it 

 was not imagined that the vibrations of light could be 



* Letter to Lange: " Gescliichte des Materialismus," . zweite Aufl. t 

 vol. ii., p. 521. 



f Nineteenth Century, September, 1878. 



