The Organism and its Chemistry 105 



mother-substance, the zymogen, of the clot-inducing sub- 

 stance is not simple but is a compound of the enzyme and an 

 inhibitant for that enzyme. By proper treatment of the 

 water extract of rennet with dilute acid, the enzyme is 

 liberated and the inhibitant destroyed, while if the treat- 

 ment be with dilute alkali the enzyme is destroyed and the 

 inhibitant liberated. But if the solutions containing the 

 two opposing substances are mixed, recombination takes 

 place and the resulting solution has the attribute of the 

 original water solution of rennet, namely, that of clot-pro- 

 duction to a sliglit degree only. 



To be specially noted is tlie fact that the inhibitant of a 

 given rennet neutralized the enzyme of that same rennet. 

 Now comes the thing of special importance from the stand- 

 point of comparative zoology : When solutions of both en- 

 zymes and inhibitants are prepared from different species 

 of animals (the calf, the jjig, the guinea pig, and the pika, 

 were used in the experiments), it turns out that tlie in- 

 hibitant from the rennet of one species does not inhibit the 

 enzyme from the rennet of another species. And so it is 

 concluded that ''both the enzyme and the inhibitant are dif- 

 ferent for each animal, a fact of great interest and impor- 

 tance," to repeat Harden's words. 



Special attention should be called to the circumstance that 

 not only is this another method of differentiating species 

 chemically, but that it is an exceedingly delicate me'thod. 

 This is particularly seen in the fact that the rennets of the 

 species investigated were found capable of clotting cow's 

 milk in spite of their being different in other respects as 

 just shown, it being thus revealed that the fact that rennets 

 from two different animals may act alike on cow's milk, 

 does not prove them to be alike in all their attributes. No 

 careful student of nature will ever neglect the principle 

 involved in this. We may take this as an impressive re- 

 minder that the problems of the dependence and the inde- 



