CLASSIFICATION OF INFECTIOUS DISEASES 125 



which a certain preventive or curative method should be 

 capable of yielding in each particular case. By proceeding 

 in this way, we ought little by little to make therapeutics an 

 exact science. 



Thus, for example, the fact that in diphtheria the antigen 

 in excess forms with the normal antibody a pathogenic com- 

 pound while the antigen with antibody in excess forms a 

 compound which is neutral for the organism, permits us to 

 conclude that preventive or curative treatment by antitoxic 

 serum is the most efficacious method. And we should con- 

 clude that in all other cases when reactions between anti- 

 bodies and antigens are of the same nature the same treat- 

 ment will yield analogous results. On the other hand where 

 the antibody in excess forms with the antigen an insoluble 

 compound and where it is precisely this excess of antibody 

 which is the cause of the pathologic manifestations (ana- 

 phylactic state) (as in typhoid fever) the disease cannot be 

 treated by injections of antibody, which already exist in 

 excess but, on the contrary, must be treated by anti-anaphyl- 

 actic methods that is, by injections of antigen which will 

 neutralize this excess of antibody. 



There are diseases in which the antibody in excess neutral- 

 izes the antigen without producing appreciable disturbances 

 and there are others in which the antibody in excess, while 

 neutralizing the antigen, produces by its combination with 

 the latter a pathologic reaction. This difference between the 

 properties of the compounds of antigens with their antibodies 

 in excess allows us to divide the known diseases into two 

 great groups. Our knowledge of the properties of antibodies 

 and of antigens as well as of the compounds formed by these 

 two substances is altogether too incomplete in most cases 

 for us to assign at the present their exact place in each dis- 

 ease. Judging from what we actually know, we can group 

 together on the one hand, diphtheria, tetanus, certain pneu- 

 monias, perhaps anthrax fever, erysipelas, and certain cere- 

 brospinal meningitides in which the antigen acts directly and 

 rapidly on tissues and is neutralized by the antibody in 

 excess without anaphylaxis and, on the other hand, all the 

 other septicemias in which the incubation period is more 



