47 



races " of certain other bacterial species, that these serological 

 differences are unimportant therapeutically, or that they are 

 merely minor idiosyncrasies which needlessly distract attention 

 from the identity of the strains in more essential biological 

 functions, such as toxicity. Theoretically, it may be reasonable 

 to argue that antigenic differences are not all of equal importance. 

 A protein compound may possess a large number of special 

 chemical groups, and the particular configuration of one of these 

 groups may determine whether it is acted upon by a certain 

 enzyme or not ; but the configuration of the other special groups 

 may be of no importance to the enzyme. Similarly, though 

 the therapeutic value of an antiserum may be correlated with 

 some special chemical group in the antigen, it does not follow 

 that it is correlated with each of the antigenic characters which 

 may be demonstrated by agglutination or precipitation. But, 

 with pneumococci, the practical difficulty is to find laboratory 

 data which will enable one to discriminate between important 

 and unimportant antigenic differences ; and this difficulty has 

 not yet been overcome. 



The significance of serological types of pneumococci therefore 

 demands serious consideration. The subject raises many immun- 

 ological problems and may be discussed from many aspects 

 which I have not attempted to deal with in this report. All 

 I propose to do is, first to call attention to certain general ideas 

 about antigens and antibodies, and then to apply these considera- 

 tions to a practical question. Neufeld's standpoint does not 

 appear to hold out prospects of further progress; can one find 

 a wider outlook which will give a more helpful view as to the 

 significance of pneumococcal antigens ? 



General Ideas about Antigens and Antibodies. 



General ideas must be handled with caution. For example, 

 it does not follow that what is known about the antigenic 

 properties of serum or other non-bacterial protein can be applied 

 in every detail to bacterial antigens ; and, again, the antigenic 

 characters which are of importance in preparing a serum which 

 will prevent or arrest invasion by parasitic bacteria are not 

 necessarily the same as those which are of predominant influence 

 in the serological classification of bacterial races by means of 

 the agglutination test. 



So preliminary ideas may give rise to further questions as 

 to how far principles based on one kind of work (e.g., specific 

 tests for blood serum) are applicable to another branch of 

 immunity (e.g., the production of antibacterial sera). With 

 this understanding, I begin by borrowing freely from the facts, 

 theories, and suggestions which have been put forward by 

 biochemists in their studies of non-bacterial antigens. In what 

 follows, Pick's valuable survey of the subject has been parti- 

 cularly helpful.* 



* Kolle and \yassermann's- Handbuch der pathogenen Mikroorganismen, 

 2nd Edition, Vol. I, p. 685. 1912. 



