240 Science Religion and Reality 



The principal arguments of the neo-vitalists can be stated thus : 

 (i) the argument from inconceivabihty, and (2) the " actual whole- 

 ness " of the organism. The first of these arguments they are 

 continually using, but perhaps do not realise that it is a two-edged 

 weapon and cuts both ways. As an example of the use of it we 

 have already seen how Driesch refuses to believe that any mechanistic 

 description can be adequate for the facts of development, and how 

 Haldane says the same thing for the mechanisms of adjustment to 

 slightly abnormal conditions in the adult animal. We shall see 

 later whether these are really so inexplicable as they would have us 

 believe. But the fundamental fallacy of the argument from incon- 

 ceivability is quite a simple one. There are not a few occasions 

 in the history of biology in the last fifty years on which one ex- 

 perimentalist has brought forward a mechanistic theory to account 

 for facts which he has observed, and another has proved that the 

 theory in question is insufficient to account for them. Out of 

 many examples we may take the work of Rhumbler on amoeboid 

 movement. Amoebae, the very low unicellular organisms which 

 live in ponds on dead leaves, progress by alternately putting out and 

 retracting protoplasmic processes called pseudopodia and pulling 

 themselves along. Rhumbler developed a theory to explain these 

 facts which made use of physical conceptions only, such as surface 

 tension. Later, however. Mast, Root, and other biologists in the 

 U.S.A., discovered certain other facts which Rhumbler's theory 

 would not cover, and it had to be abandoned. Naturally the 

 vitalists nude much of this failure, and the general assumption 

 was that because a mechanistic theory had hopelessly broken down, 

 therefore no mechanistic theory that might be proposed in the 

 future would ever fit the facts. A most obvious logical error. 

 We do not even know what the face of physics and chemistry 

 themselves may be like in twenty or thirty years — they may even 

 have the same face. How, then, can we maintain that a mechanistic 

 explanation is inconceivable, as the neo-vitalists continually 

 do ? No, all we can do is to express our opinion one way or the 

 other according to what seems to us most likely. Whichever we 

 do, belief will be necessary, and the biologist can either believe that 

 in time physico-chemical explanations — ^and be it noted, in terms 

 of the physics and chemistry of the period, and not in those of to-day 

 — will be capable of describing all the phenomena of bodily life ; 

 or, on the other hand, he can believe that an immaterial ghost 



