VIRCHOW AND EVOLUTION. zSg 



cess of time, vitality will follow the example of motion, and, after the 

 necessary antecedent wrangling, take its place among the attributes 

 of that " universal mother " who has been so often misdefined. 



That " matter is not itself alive " Prof. Knight seems to regard as 

 an axiomatic truth. Let us place in contrast with this the notion en- 

 tertained by the philosopher Ueberweg, one of the subtilest heads that 

 Germany has produced : 



" What occurs in the brain would, in my opinion, not be possible, if the 

 process which here appears in its greatest cojicentration did not obtain gener- 

 ally, only in a vastly diminished degree. Take a pair of mice and a cask of 

 flour. By copious noiu-ishment 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 must 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 concentrated 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, preexisting, but diluted in the 

 food. 



" Definitions," says Mr. Holyoake," " grow as the horizon of experi- 

 ence expands. They are not inventions, but descriptions of the state 

 of a question. No man sees all through, a discovery at once." Thus 

 Descartes's notion of matter, and his explanation of motion, would be 

 put aside as trivial by a physiologist or a crystallographer of the pres- 

 ent day. They are not descriptions of the state of the question. 

 And yet, it may be said in passing, a desire sometimes shows itself in 

 distinguished 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 mathe- 

 maticians." That definitions should change as knowledge advances is 

 in accordance both with sound sense and scientific practice. When, 

 for example, the tmdulatory theory was started, it Avas not imagined 

 that the vibrations of light could be transverse to the direction of propa- 

 gation. The example of sound was at hand, which was a case of lon- 

 gitudinal vibration. Now, the substitution of transverse for longitu- 

 dinal vibrations in the case of light involved a radical change of con- 

 ception as to the mechanical properties of the luminiferous medium. 

 But, tliough this change went so far as to fill space with a substance 

 possessing the properties of a solid, rather than those of a gas, the 

 change was accepted, becausg the newly discovered facts imperatively 

 demanded it. Following Mr. Martineau's example, the opponent of the 



■ Letter to Lange, " Geschichte des Materialismus," zweite Aufl., vol. ii., p. 521. 

 - Nineteenth Century, September, 18'78. 



