CLASSIFICATION OF INFECTIOUS DISEASES 127 



the nature and the localization of the sensitive cells and in 

 consequence by the lesions produced especially by the 

 rapidity of the evolution because the bacteria of these dis- 

 eases are less easily adapted to the infected medium than 

 those of tuberculosis or of syphilis. 



SUMMARY. From the point of view of their evolution, all 

 infectious diseases have as a common characteristic the 

 formation of antibodies in excess under the action of antigens. 



The common distinguishing characteristic between the 

 different diseases lies in the physicochemical nature and the 

 biologic properties of the compounds formed by the action 

 of the antibodies in excess with their antigens. These com- 

 pounds may be either soluble and neutral and here the 

 immunizing action of the antigens will confer on the organ- 

 ism immunity without anaphylaxis (diphtheria); or com- 

 pounds may be insoluble and pathogenic and here the immun- 

 izing action of the antigen confers on the organism immunity 

 and also anaphylaxis (almost all septicemias) . 



The two great families of infectious diseases can be sub- 

 divided according to the affinities of antigens, the relative 

 quantity of antibodies produced, and the duration after 

 recovery of the production of antibodies. This latter prob- 

 ably depends upon the nature and upon the role which the 

 mother substance of the antibody fulfills in the life of the 

 cell. 



In the second great group three types can be distinguished : 



1. Tuberculosis. 



2. Typhoid fever. 



3. Gonorrhea, aphthous fever, and a subtype; syphilis and 

 malaria. 



The species in these groups may be differentiated and 

 characterized by the affinities of antigens for different 

 tissues, by the nature of lesions produced and by the adapta- 

 tion of bacteria to their host. 



