THE GERM-PLASM THEORY 375 



one received the ' red,' the other the ' black ' determinants. Our eyes 

 can perceive no difference between the nuclear substance of the tM^o 

 cells, but the same is true of the chromosomes of the paternal and 

 maternal nuclei in the fertilized ovum, although we know in this 

 case that they contain different tendencies. In any case we are not 

 justified in concluding from the apparent similarity of the chromo- 

 some-halves in nuclear division that there cannot be differential 

 division. The theoretical possibility that there is such differential 

 division cannot be disputed ; indeed, I am inclined to say that it 

 is more easily imagined than the division of the ids into absolutely 

 similar halves. Both are only conceivable on the' assumption that 

 there are forces which control the mutual position of the determinants 

 in the ids, that is, on the assumption of ' affinities.' I shall not follow 

 this further, but that there are forces operative within the ids which 

 are still entirely unknown to us is proved at every nuclear division 

 by the spontaneous splitting of the chromosomes. 



It has been objected to my theory that such a complex whole as 

 the id could not in any case multiply by division, since there is 

 no apparatus present which can, in the division into two daughter- 

 units, re-establish the architecture disturbed by the growth. But 

 this objection is only valid if we refuse to admit the combining 

 forces, the ' vital affinities ' within the ids, and the same is true for 

 the smaller vital units. An ordinary chemical molecule cannot 

 increase by division ; if it be forcibly divided it falls into different 

 molecules altogether ; it is only the living molecule, that is, the 

 I dopho r, which possesses this marvellous pr operty of j ^rowth and 

 division into two halves similar to itselt and to the ancestral mole- 

 cule, and we may argue from this that in the division of the ids 

 forces of attraction and repulsion must likewise be operative ^. 



I see no reason why we should not assume the existence of such 

 forces, when we make the assumption that the hundreds of atoms 

 which, according to our modern conceptions, compose the molecule of 

 allmmeii and determine its nature, are kept by affinities in this 

 definite and exceedingly complex arrangement. Or must we suppose 

 that between the atom-complex of the molecule and the next higher 

 atom -complex of the biophor, determinant, and id there is an absolute 

 line of demarcation, so that we must assume quite different forces in 

 the latter from those we conceive of as operative in the former ? The 



^ In my book The Germ-Plasm I have already assiimed tlie existence of ' forces of 

 attraction ' in the determinants and biophors, as in the cells. I did not, indeed, enter 

 into details, but I argued on the same basis as now {Germ-Plasm, p. 64, English edition). 

 My critics have overlooked tliis. 



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