566 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



lated also from various other microorganisms, especially from streptococci. 



Recent studies of proteins make it very probable that in the organism the 

 simpler peptid chains are present, not as such, but in association with one 

 another, and it has been suggested that their molecular weights are multiples 

 of a unit possessing a molecular weight of 34,500 (Svedberg). Reversible 

 associations and dissociations may take place. According to Bergmann, such 

 a unit is built up of 288 amino-acid residues and a protein may consist of 

 multiples of such units. Within these units certain amino acids recur at 

 regular intervals, which are characteristic of different proteins. X-ray studies 

 make it probable, moreover, that such protein chains may be folded and that 

 parallel fibers may be linked together by means of their active sidechains in defi- 

 nite patterns, the distance of these chains being ascertainable by the X-ray pat- 

 tern (Meyer and Mark, Astbury). According to Mirsky and Pauling, these 

 sidechains are united by hydrogen bonds between the peptid nitrogen and the 

 oxygen of the carboxyl group. 



Denaturation by heat, application of alkali, acid or various other means, 

 is supposed primarily to bring about breaks in these sidechain bonds and to 

 unfold the main chains. Denaturation also alters or reduces the specificity of 

 the proteins ; it may diminish or destroy the specificity of the antigens and it 

 destroys the individuality differentials. Conversely, in accordance with this 

 theory of protein structure, we may assume that the specificity, and in par- 

 ticular, also the specific character of the individuality and species differentials, 

 depend upon the character and distribution of these patterns and linkages as 

 well as on the chemical constitution of the amino-acids ; and it may further- 

 more be suggested that some of these factors are specific for cell and blood 

 proteins in different individuals; also, that all the cell proteins in the same 

 individual must have a certain characteristic in common, which differentiates 

 these proteins from the proteins of all other individuals. At present it seems 

 impossible to do more than to make this general statement concerning the 

 possible connections between the nature of the individuality differentials and 

 theories of protein structure, of which several have been proposed. 



There is a second series of investigations which may throw some light on 

 the structure of various differentials, although they have more significance 

 for the organ, heterogenetic and blood-group differentials than for the 

 organismal differentials. These investigations, to which we have already re- 

 ferred, deal with the experimental modification of antigens and the corre- 

 sponding changes in the immune substances which are elicited by the injection 

 of the modified antigens. This method of research was inaugurated by 

 Obermayer and Pick, who thus laid the foundation for the subsequent 

 fargoing analysis of the chemical nature of antigens. It is of interest, in this 

 connection, that the discovery of Jacques Loeb of the possibility of inducing 

 heterogenous fertilization by addition of alkali to the medium in which the 

 germ cells are suspended, and thus of modifying the specificity of the fertiliza- 

 tion process, suggested to Obermayer and Pick the thought that also the 

 antigen specificity might be accessible to changes by chemical means. They 



