INTRODUCTION 



Despite these facts, the property which makes certain bacterial con- 

 stituents antigenic must play a definite role in the biology of a bac- 

 terium. Of these constituents, protein is the most essential one. It is 

 not an exaggeration if we make the statement that life could not have 

 appeared without protein substances. The proteins of the most primi- 

 tive forms of life which have appeared as single cells in the evolution- 

 ary scale of living forms must have possessed attributes responsible for 

 the antigenic property long before the appearance of animal hosts 

 which alone have served as the means of exposing it. 



Certain bacterial protein substances, as well as those of animals and 

 plants, would appear to be endowed with catalytic powers which are 

 essential for the physiological functions of the living forms from which 

 they are derived. Likewise, catalytic power, as discussed in this treatise, 

 appears to stimulate, or is responsible for the formation of specific anti- 

 bodies in animals to proteins and also to certain non-protein compo- 

 nents. From the standpoint of the biology of bacteria these facts would 

 seem to represent a contradiction; nevertheless it is a fact that chemical 

 forces of bacteria (or their constituents) which accelerate their in vitro 

 activities, as well as their invasive, infectious and growth activities in 

 a host, are also instrumental in setting up in the host highly specific 

 antagonistic immune mechanisms which block or neutralize these very 

 activities of bacteria. The highly specific nature of these relationships, 

 characteristic of enzyme reactions, are strong indications that the 

 mechanism of the above mentioned bacterial activities are of catalytic 

 nature. 



The action of enzymes usually results in the formation of reaction 

 products which specifically inhibit the action of these enzymes. Simi- 

 larly, as discussed in this treatise, antigens as enzymes, or enzymes as 

 antigens, produce antibodies, as finished reaction products, the only 

 function of which, as far as our present knowledge goes, is to neutralize 

 the specific biological activities of antigens. 



Practically all proteins foreign to the species possess a special sort 

 of biocatalytic power, namely that of stimulating and directing specif- 

 ically the synthesis of antibody. This familiar property of antigenicity 

 must be considered a special kind of biocatalytic power, and it is pos- 

 sessed by enzyme proteins, in common with other proteins. Since we 

 are at present in the dark concerning the specific functions of the latter 

 proteins in the living cells, it is premature to consider them devoid of 



