THE LAWS OF SPECIFICITY. 5 



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 succumbed 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 antitoxic or agglutinating prop- 

 erties 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, all 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 performed 

 with the typhoid bacillus, and cholera antibodies only when performed with 

 the cholera vibrio. Substances which lack this essential property of speci- 

 ficity 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 fundamental principle of serum diagnosis. As 

 soon as the specificity of a reaction becomes doubtful, its diagnostic im- 

 portance 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 discussion, the absolute necessity of these control tests must be 

 urged, even though it may appear superfluous to the beginner, when for 

 apparently simple experiments controls are performed which consume more 

 time than the actual diagnostic test itself. Probably also the desire will 

 arise, and perhaps be satisfied, to omit these control experiments. This 

 done, notwithstanding of a possibility to obtain for even a long time, per- 



