Chemical Basis of Genus and Species 61 



that the fossil forms of invertebrate animals and of algae 

 and bacteria, which Walcott found in the Cambrian and 

 which may be two hundred million years old, must 

 have had the same specificity at that time as they or 

 their close relatives have today; and this raises the 

 question: What is the nature of the substances which 

 are responsible for and transmit this specificity? It is 

 obvious that a definite answer to this question brings 

 us also to the very problem of evolution as well as that 

 of the constitution of living matter. 



There can be no doubt that on the basis of our present 

 knowledge proteins are in most or practically all cases 

 the bearers of this specificity. This has been found 

 out not only with the aid of the precipitin reaction but 

 also with the anaphylaxis reaction, by which, as the 

 reader may know, is meant that when a small dose of 

 a foreign substance is introduced into an animal a 

 hypersensitiveness develops after a number of days 

 or weeks, so that a new injection of the same substance 

 produces serious and in some cases fatal effects. This 

 hypersensitiveness, which was first analysed by Richet, * 

 is specific for the substance which has been injected. 

 Now all these specific reactions, the precipitin reaction 

 as well as the anaphylactic reaction, can be called forth 

 by proteins. Thus Richet, in his earliest experiments, 

 showed that only the protein-containing part of the 

 extract of actinians, by which he called forth anaphy- 



1 Richet, C., L'anaphylaxie. Paris, 1912. 



