THE LAW OF SPECIFICITY 5 



bacillus. Rabbits rendered actively immune by inoculation with extracts of hog- 

 cholera bacilli possess a serum which when injected into an animal of a different species, 

 as the guinea-pig, will render the latter passively 'mmune. If, however, the serum is 

 injected into another animal of the same class (another rabbit), no protective power is 

 transmitted. In other instances it was shown that the rabbit which was being treated 

 with the purpose of active immunity was in reality never immune, as it always suc- 

 cumbed when injected with living bacteria even though its serum contained bodies 

 which were perfectly able to passively protect guinea-pigs against the same deadly 

 infection . 



Just as it is incorrect to consider an antibody and protective body as 

 one and the same thing, it is equally erroneous to deny the existence of 

 protective bodies, because their presence cannot be demonstrated by a 

 certain method of laboratory examination. It must be kept in mind 

 that there are still many unsolved problems in the subject of immunity 

 and that therefore only the positive findings should be the basis for drawing 

 conclusions. 



In order to learn the nature of these antibodies attempts have been 

 made to isolate them chemically. Thus far all such trials have been 

 unsuccessful. It is even uncertain whether these so-called antibodies are 

 definite chemical entities. Only the effects of the serum as a whole are 

 known, and the ingredients in it to which these activities are attributed 

 are thought of as antibodies. For didactic purposes antibodies, as 

 antitoxins, agglutinins, etc., will be spoken of in this book when the anti- 

 toxic or agglutinating properties, exclusively, are meant. 



In spite of the individual differences which are ascribed to the 

 The Law of various classes of antibodies, there is one quality possessed by 

 Specificity. a ll their specificity. To explain this by a rather crude 

 example, may be mentioned the fact that typhoid antibodies 

 will give their various reactions of immunity only when these are per- 

 formed with the typhoid bacillus, and cholera antibodies only when per- 

 formed with the cholera vibrio. Substances which lack this essential 

 property of specificity cannot be considered antibodies, although they 

 may fulfill all other requirements. There are indeed limitations to this 

 fast rule, but these will be considered subsequently. ' For the present 

 the following can be taken as a fixed fact; namely, that every true 

 antibody is absolutely specific, and that all substances or bodies which are 

 not specific cannot be real antibodies. The law of specificity is the funda- 

 mental principle of serum diagnosis. As soon as the specificity of a reac- 

 tion becomes doubtful, its diagnostic importance suffers greatly. In 

 the following pages, therefore, the question whether or not a reaction is 

 specific will be repeatedly discussed, and it will be the aim in every way 

 possible, especially by the use of control tests and experiments to outline 

 the limits of this specificity. Here, even at so early a stage of the discus- 



