HEREDITY FROM PHYSICO-CHEMICAL POINT OF VIEW. 75 



the same genus. The growing crystal takes on a definite "spe- 

 cies-specific" form, in a manner suggesting a close analogy to 

 the growing germ; this definite form is the expression of the 

 specific properties of the protein molecule, and is presumably 

 dependent upon its special stereochemical configuration. It is 

 well known that molecules of similar stereo-structure tend to 

 segregate in the process of crystallization ; thus in the crystalliza- 

 tion of a racemic tartrate from its solution one group of crystals 

 is formed exclusively or at least predominantly of molecules 

 of the dextro-tartrate, the other of the Isevo-tartrate, although 

 in respect to solubility and other physico-chemical properties 

 the two compounds are identical. In such an instance it is quite 

 certain that similarity of stereo-structure is the critical factor 

 determining the union of the dextro-molecules to form a definite 

 crystalline aggregate specifically distinct from that formed by the 

 laevo-molecules. 1 



The physiological properties of the two stereo-isomers are 

 correspondingly unlike; fermentability and related properties 

 (such as general assimilability and pharmacological action) have 

 been shown to differ markedly in a large number of pairs of 

 asymmetric compounds, a clear proof that the activity of living 

 protoplasm is largely conditional upon the specific space-relations 

 of the atoms composing the physiologically active molecules. 

 This is particularly true of compounds entering into metabolism : 

 thus we know that enzyme action is determined by stereo- 

 structure. Perhaps the clearest proof that specific constructive 

 metabolism is similarly determined is furnished by the specific 

 character of the metabolic response following the introduction 

 of protein antigens into the organism- i. e., by the specific char- 

 acter of the anti-bodies produced. These new compounds, evi- 

 dently synthesized by the living cells, exhibit specific chemical 



1 Thus the introduction of a crystal of the laevo form into a supersaturated 

 solution. of racemic tartrate causes the separation of laevo-tartrate alone; similarly 

 dextro-crystals separate out dextro-tartrate (cf. Gernez: Comptes rendus, 1866, Vol. 

 63, p. 843). The recent work of Marc indicates that in general crystallization is 

 preceded by an adsorption; and that crystals, when used as adsorbents, adsorb by 

 preference substances which crystallize in a similar form. /. e., the similarity in 

 the spatial configuration of the molecules is what determines their union to form 

 larger 'aggregates (cf. Marc: Zeitschr. physik. Chem., 1913, Vol. 81, p. 641; also 

 ibid., 1911, Vol. 75, p. 710, and earlier papers there cited). 



