December 2, 1904.] 



SCIENCE. 



747 



ferentiation occurs. In my view the ma- 

 terial of the new stump is at first totipotent 

 (at least for each kind of material) ; the 

 surface and the ends of the old organs are 

 the terminals between which the segrega- 

 tion of the new parts takes place. 



Let us next turn our attention for a 

 moment to the factors that determine the 

 organization of the new structure. 



The term formative force was formerly 

 used to cover the changes that take place 

 when the new organ 'crystallizes,' as it 

 were, in the new material. Since no such 

 force is known in the physical world, mod- 

 ern biologists have looked askance at the 

 term. In one sense they are, of course, en- 

 tirely justified in doing so, because no such 

 creating force is known to us outside of the 

 phenomena to be explained, and the term, 

 therefore, only restates the changes and 

 can not be used as a causal explanation of 

 them. In another sense, however, the use 

 of this term may come nearer to an expres- 

 sion of what is needed than any attempt 

 to explain the results by known chemical 

 or physical 'forces' or energies or prin- 

 ciples ; for it seems to me that we are deal- 

 ing here with a phenomenon characteristic 

 of living material — a phenomenon that is 

 unknown to the physicist. This does not 

 mean that I believe the phenomenon is not 

 capable of a causal, i. e., of a physical, ex- 

 planation. In fact, I have every reason 

 to believe it belongs to this category, but 

 it is not a principle that the physicist meets 

 with, or, at least, has yet met with out- 

 side of living material— unless, indeed, the 

 so-called liquid crystals of Lehmann repre- 

 sent a similar phenomenon. 



The term 'formative force' is obnoxious 

 also because of the dubious use of the 

 word force. It has been pointed out that 

 since no two animals develop in the same 

 way, or regenerate identical structures, 

 there would be as many kinds of formative 

 forces as there are animals that develop or 



regenerate. In fact, there would be in 

 each animal as many kinds of formative 

 forces as there are parts that can regen- 

 erate. I believe the objection is well 

 founded, at leasts to the extent that it 

 shows that we are not offering a causal ex- 

 planation when we refer the phenomens to 

 a formative force. On the other hand, 

 no one knowing the facts can doubt that 

 all the cases belong to the same general 

 category: but since the composition of no 

 two animals belonging to different species 

 is the same we should not expect the egg 

 or the newly formed materials to organize 

 themselves in exactly the same way, 

 although the kind of action may be the 

 same in all of them. 



We meet with the same problem in at- 

 tempting to explain certain facts in in- 

 organic nature. The salts of different sub- 

 stances crystallize each in its own peculiar 

 way. It would, therefore, be just as mis- 

 leading to speak of a crystallizing force as 

 of a formative force, yet no one doubts 

 that the crystallization of each salt de- 

 pends on some property that all salts have 

 in common. 



We meet here with a philosophical prin- 

 ciple that it would be out of place to dis- 

 cuss at this time, yet it is a point of as 

 much importance to the practical, thinking 

 experimentalist as to the theorist. I sug- 

 gest that, for want of a better term, we 

 may provisionally call the property of liv- 

 ing material to assume a specific form the 

 property of formative organization. 



I may sum i^p my conclusions categor- 

 ically as follows: 



1. AA^iere no alternative exists at a cut 

 surface there is no question of polarity 

 and we have simply to deal with the phe- 

 nomenon of formative organization, which 

 I would suggest, but can not prove, is in 

 some way a phenomenon of contraction de- 

 pending on the relative condition of ten- 

 sion in the parts. 



