576 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



stance into active enzyme by an autokatalytic reaction. But this latter type of 

 reaction shows only a very imperfect specificity. Pepsin transforms pepsinogen 

 into pepsin, and trypsin causes the activation of trypsinogen, but trypsin 

 exerts the same function also towards chymotrypsinogen. While thus the 

 activating enzyme possesses only a limited specificity, the substratum on 

 which the enzyme acts — in this case the precursor substance — undergoes spe- 

 cific changes ; thus chymotrypsinogen can only be converted into chymotrypsin, 

 whatever the nature of the activator may be. 



In those enzymes which consist of a combination of a protein and a 

 prosthetic group, specificities in the character and action of the enzymes may 

 depend not only upon the nature of the protein but also upon differences in 

 the prosthetic group, or in the manner in which the prosthetic group and the 

 protein are linked. Specific differences in the production of such enzymes in 

 different cells may, according to Robbins, depend upon the different ability 

 of different cells to produce a vitamin which forms a constituent part of the 

 enzyme. As to the relations between enzymes and organismal differentials, 

 nothing is known in regard to individuality differentials in enzymes. How- 

 ever, there is reason for assuming that the corresponding enzymes of dif- 

 ferent species are distinct, although such differences cannot always be dem- 

 onstrated by means of immune reactions. Thus Kirk and Sumner could not 

 definitely distinguish between the urease of soy bean and of jack bean by 

 means of the precipitin reaction or by using the protective action of immune 

 sera as a test. But that species differences exist has been shown through a 

 study of the solubilities of various enzymes ; for example, the solubilities of 

 cattle and swine pepsin differ from each other. In certain instances a species- 

 specificity has been demonstrated also by the production of immune substances, 

 especially of precipitins, and of localized anaphylaxis in the guinea pig. Ten 

 Broeck used the uterus of the guinea pig as test organ and was able to dis- 

 tinguish between trypsin from cattle and swine and also between chymotrypsin 

 and chymotrypsinogen. Seastone and Herriot, by means of the precipitin re- 

 action, could distinguish swine, cattle and guinea pig pepsin from rabbit and 

 chicken pepsin; but pepsin from swine, cattle and guinea pig could not be 

 differentiated from one another by these means. On the other hand, pepsin 

 and pepsinogen could be distinguished by the use of the precipitin reaction. 

 Moreover, precipitins for enzymes did not react with serum proteins of the 

 corresponding species. It may therefore be concluded that the proteolytic 

 enzymes of the pancreas and stomach, and their precursors, possess substance 

 and organ specificity; furthermore, that the corresponding enzymes and 

 their precursors from different species differ in their constitution; but no 

 proof has been given so far that this difference corresponds to the graded 

 relationship of the various species, or that these enzymes have a chemical 

 characteristic in common with proteins in other organs of individuals be- 

 longing to the same species ; nor has it been shown that they possess indi- 

 viduality differentials. 



We have mentioned already that in the process of transformation of the 

 precursor substance into the active enzyme, the specificity resides in the 



