154 CHEMICAL STATICS 



a simple and readily intelligible explanation of an otherwise 

 exceedingly puzzling fact. I refer to the individuality of the 

 tissues and tissue-fluids. Despite the fact that the individual 

 proteins which are found in the tissue-fluids of tolerably nearly 

 related animals (e.g., the mammalia) appear, on analysis, to be 

 identical with one another,* yet the tissue-fluids of one mammal, 

 when injected into the circulation of another, are treated as 

 foreign intrusions and give rise to "antibodies"; while the indi- 

 vidual protein constituents of these fluids are also treated as 

 foreign matter when introduced into the circulation, giving rise 

 to " precipitations " and to phenomena such as " anaphylaxis " 

 (120). 



On the basis of the view developed above, however, not only 

 the constitution of the individual components of the protein 

 complex is of importance in determining its characteristics, but 

 also the relative proportion of these components.! Two protein- 

 complexes of this type might well be built up out of identical 

 units and yet differ fundamentally owing to differences in the 

 combining proportions and, consequently, in the mode of linkage 

 of these units. Any one constituent of the complex would, of 

 course, be a totally different substance from the complex itself 

 and its introduction into the tissues or tissue-fluids would result 

 in a more or less extensive disruption of the equilibrium of which 

 the complex is an expression and which lends it, in each tissue, 

 tissue fluid and species, its own distinctive character. 



In pursuance of this idea Gay and Robertson (32) (33) and 

 C. L. A. Schmidt (110) (111) have investigated the antigenic 

 properties of several compound proteins. If compound proteins 

 differ in their biological specificity from their constituents then 



* Thus the casein of human milk is chemically identical with the casein of 

 cows' milk and with that of goats' milk (2) (1). The fibrin of ox-blood ap- 

 pears to be identical with that of horse-blood (4). The serum albumins and 

 globulins of goose-blood are identical with those of horse-blood (3). Whether 

 chemically identical proteins derived from different animal species are also 

 antigenically identical or not has not yet been satisfactorily established. 



t Just as the different proteins and polypeptids are built up out of very 

 similar amino-acids and yet differ widely from one another in their character- 

 istics because the proportions in which the amino-acids enter into the mole- 

 cules are different. These protein-complexes may be regarded as bearing the 

 same relationship to the simple proteins which they yield on decomposition as 

 the polypeptids do to the amino-acids. 



