HEREDITY FROM PHYSICO-CHEMICAL POINT OF VIEW. 73 



cally, although otherwise closely similar e. g., haemoglobins 

 from different species tend to form crystals, i. e., structural 

 aggregates, -which are specifically distinct in their form-charac- 

 ters. 1 A definite relation between the chemical specificity and 

 the structure-forming properties of these colloids is thus indi- 

 cated. The relation of proteins to organic structure therefore 

 requires special consideration in any theory of heredity. 



The proteins form the colloids out of which, together with 

 certain other associated materials, chiefly lipoid, the more per- 

 manent or stable, i. e., "structural" portions of most living or- 

 ganisms, and especially the cell-structures, are built up. The 

 relations of these substances to the specific characters of the 

 organism must for this reason be recognized as peculiarly inti- 

 mate, even though we are not yet in a position to understand the 

 exact relationship between a particular type of structure in an 

 organism and the specific peculiarities of the protein composing 

 that structure. The available evidence indicates, however, that 

 a definite relationship of this kind does exist. We know for 

 example that the presence of foreign proteins is often incompatible 

 with the preservation of normal structure in cells; the cytolytic 

 action of foreign blood-sera, and the formation of specific cyto- 

 lysins when cell-proteins are used as antigens, show that so funda- 

 mental a character as the semi-permeability of the plasma-mem- 

 brane in a cell is dependent upon the specific peculiarities of its 

 constituent proteins. And in all cell-structures it is probable 

 that a similar relation exists. Such facts indicate clearly that 

 the specific structure of a cell or organism depends upon the 

 chemical specificity of its structural proteins. Now the term 

 specificity, as applied to the individualized character of an or- 

 ganic species, has its morphological and physiological as well as 

 its chemical significance: i. e., each species has its own special 

 form and structure and its own characteristic modes of activity 

 and behavior, as well as its own distinctive and unique chemical 

 composition. But according to the present conception it is the 

 chemical specificity which forms the basis of the other two, and 



1 Cf. Reichert and Brown: "Differentiation and Specificity of Corresponding 

 Proteins and other Vital Substances in Relation to Biological Classification and 

 Organic Evolution: the Crystallography of Haemoglobins." Carnegie Institution 

 of Washington, 1909. 



