390 SCIENCE PROGRESS 



been maintained that this implies as many distinct controlling 

 principles as there are kinds of organisms or even individuals ; 

 but this is surely a mistake. It is equally possible that the 

 material at the disposal of the principle controlling develop- 

 ment will determine the form it takes, as the circumstances 

 which surround a man determine his action, without being the 

 final "cause" in either case. A man who wants to build a 

 house will build one of wood in a land where trees are plentiful 

 and stones scarce, yet no one will say that the abundance of 

 trees is the cause of his building the house. So the principle 

 controlling development may cause a star-fish to develop from 

 one kind of ovum and a dog from another, not because the 

 principle is different but because the ovum of each is adapted 

 only to the production of that kind of result. 



Further, it should be noticed that one objection often brought 

 against vitalism is not valid against this suggestion, the argu- 

 ment, namely, that many substances formerly believed to be 

 produced only by living organisms have now been synthesised 

 in the laboratory and that others, which now defy the chemist, 

 may be conquered to-morrow. A plant, by its control of certain 

 chemical energies, causes the production of the compound indigo. 

 The chemist analyses the natural compound and proceeds to 

 sythesise it in his laboratory. This, however, is no proof that 

 the compound can ever occur in nature in the absence of life, for 

 the chemist imitates the plant in allowing certain energies to 

 come into play and keeping away others which would interfere 

 with the action if they were present. No " vital energy " is 

 required ; if energy is needed from outside he turns on his 

 gas-burner and applies a flame to his test-tube, so obtaining 

 from chemical combination a supply which would have remained 

 potential but for his intervention. 



It can hardly be doubted that the recognition of a principle 

 of this kind, which unconsciously, perhaps — or at least not con- 

 sciously in the sense in which man uses the word of himself — 

 seeks to produce individuality out of incoherence and self- 

 expression through material form would greatly simplify many 

 of the more difficult problems of biology. It is generally rejected 

 by biologists, partly because of the very real danger that if 

 it were recognised every unexplained phenomenon might be 

 ascribed to its action and still more because it seems to conflict 

 with the principle of non-multiplication of entities. But is it 



