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THE AMERICAN NATURALIST 



[Vol. XLVI 



kind of chemical entity which induces a specific reaction 

 of the germ sooner or later in its development. But 

 beyond this it is perfectly evident that however far back- 

 wards we may* follow such a series of unit -factors, at 

 every stage they play their specific role only in so far as 

 they form part of a still more general apparatus of 

 ontogenetic reaction that is constituted by the organism 

 as a whole. The whole of this apparatus, the entire 

 germinal complex, is directly or indirectly involved in 

 the production of every character. We find it convenient, 

 indeed necessary, to treat particular factors of reaction 

 (i. e., the " determiners") as if they were concrete and 

 separate things. Such, in fact, they may be, as already 

 indicated; but when we speak of them as ''bearers" of 

 the corresponding characters, we are using a figure of 

 speech that may be highly misleading. The reactions 

 (characters) which they call forth are not "borne by" 

 them. They appear as responses of the germinal organi- 

 zation operating as a unit-system; and it is to this sys- 

 tem as a whole that every character belongs, or by which 

 it is "borne" — if indeed we may permit ourselves to 

 employ the latter expression at all. 



The point of view thus indicated may, I think, be made 

 entirely clear by a chemical illustration. A number of 

 writers, among them Adami, G-uyer and Kossel, have 

 of late called attention to the parallel that may be drawn 

 between the physical basis of heredity and the complex 

 molecular groups of the proteins and other organic com- 

 pounds. It is a most suggestive one, though it is not to 

 be taken too literally — indeed I shall employ it only as a 

 kind of allegory or illustrative fiction. No one can fail 

 to be struck with the really remarkable analogy, in 

 method and in results, between the procedure of modern 

 genetic experiment and that of modern organic chem- 

 istry. Just as the qualities of a particular protein may 

 be definitely altered by the addition, subtraction or the 

 substitution one for another of particular side-chains or 

 molecular "Bausteine," so the addition, subtraction or 



