IMMUNITY AND ADAPTATION. 149 



antiferment acts mainly on the blood of that species which is 

 sucked by the parasite. In regard to the tissue coagulins, their 

 specificity has already been mentioned above. We might be 

 able to distinguish by the aid of this specificity for instance the 

 muscle of a lobster from that of a blue crab. In the whole, 

 however, we have to deal here rather with a class specificity than 

 with a species specificity. The specificity is not so strongly pro- 

 nounced in the case of the naturally produced antibodies as in 

 those cases in which antibodies are produced artificially. Glaess- 

 ner believes that a specificity of the antitrypsin of the blood 

 exists even among different mammalians. The number of his 

 experiments seems, however, to be very limited, so that at pres- 

 ent this specificity cannot yet be accepted as proven. It is pos- 

 sible that also in this case a class specificity does exist rather 

 than a species specificity. This may also apply to enterokinase, 

 which activates trypsinogen. A species specificity does not seem 

 to exist in this case, but a class specificity may nevertheless be 

 present. 



Both classes of substances, the experimentally produced, as 

 well as the naturally occurring substances, are specific, not only 

 in the sense that they are chemically different from substances 

 found elsewhere but that they have' a specific relationship to the 

 substance which caused their appearance and that they indicate 

 the species or class origin of this latter. Their action is, there- 

 fore, a selective one and they are not only specific in the sense 

 of being chemically different from other substances but they are 

 specifically adapted to a certain action on a very limited number 

 of substances. We may, therefore, call these substances " spe- 

 cifically adapted " substances. 



We suggested that the tissue coagulins owe their origin to a 

 process of autoimmunization, the character of a certain fibrinogen 

 determining the character of the coagulins of the same species 

 or class. Tissue coagulins resemble very closely enzymes. The 

 secretion of lactase, a typical ferment, is, as we saw, due to the 

 introduction of lactose into the organism. This suggests that 

 other ferments have a similar origin ; they may be regarded as 

 antibodies produced by a complex process of autoimmunization. 

 The existence and interaction of ferments in the animal organism 

 is perhaps the most perfect instance of internal adaptation. 



