32 PROTOPLASMIC ACTION AND NERVOUS ACTION 



and stereo-chemical configuration, by which it is dis- 

 tinguished from the corresponding proteins of even 

 nearly related species. This general fact of an associa- 

 tion between specific chemical composition and specific 

 organic structure indicates, together with other evidence, 

 that the specific chemical characters of the structural 

 proteins of any organism determine, in a manner which 

 cannot be defined in detail at present, its specific pecu- 

 liarities as an organic species/ Apparently this chemical 

 specificity determines the more intimate protoplasmic 

 structure, and hence indirectly the protoplasmic activi- 

 ties, chemical and other, which are the correlative of 

 that structure and determine ultimately the physiological 

 and other peculiarities of the species. 



The problem of the conditions of specific form- 

 determination in organisms has its special physiological 

 aspects; but on the purely physical side its closest 

 affiliations are with the problem of the relations between 

 the chemical constitution of compounds and their 

 crystalline or other molar structure. When similar 

 molecules unite to form larger molar aggregates, definite 

 regularities of form and structure usually make their 

 appearance; this is especially true when substances 

 separate from solution to form crystals; the axes and 

 angles of the crystal form are an index of the orientation 

 which the molecules assume as the aggregate is built 

 up, and of the linear proportions of the molecules. 

 In most solid compounds this association of structural 

 specificity with chemical specificity can be readily 



^ Cf. Loeb's recent discussion in his Organism as a Whole from a 

 Physico-Chemical Viewpoint, New York (191 6), chap, iii, "The Chemical 

 Basis of Genus and Species." 



