THEORIES OF IMMUNITY 31 



appreciable trouble in the organism, and the injection of the 

 apparently most innocuous albumin will disturb the normal 

 equilibrium whenever a certain dose is exceeded. 



If then we assume with Ehrlich that a cell can be attacked 

 by an antigen only in case it possesses a substance (normal 

 antibody) which has a special chemical affinity for that 

 antigen, and if we complete this hypothesis by the experi- 

 mental fact analyzed above under the name of "phenomenon 

 of surcharge" we may easily explain the immunizing and 

 pathogenic action of the antigen. This action will be exclu- 

 sively immunizing when the quantity of antigen fixed by the 

 cell does not exceed or is less than the capacity of neutraliza- 

 tion by the antibody; it will be pathogenic when a quantity 

 of antigen fixed is larger than the neutralization capacity. 

 The normal functions of the cells will then be disturbed and 

 they will suffer more or less. Experience has shown that we 

 obtain an active immunity all the more intense and all the 

 more rapidly, in other words, we obtain a quantity of "anti- 

 body in excess" all the greater, when injections are restricted 

 and when they never exceed the well-tolerated dose. We 

 may say, in a word, that immunization will be always 

 inversely proportional to intoxication or that the quantity 

 of "antibody in excess" will be directly proportional to the 

 intensity of the immunizing action of the antigen. 



The study of certain infectious diseases will permit us to 

 better define our thought. Finally, we may conclude from 

 what precedes that every pathologic state caused by an 

 antigen is determined by the reactions which this antigen 

 may provoke in the organism and that the nature and the 

 gravity of these reactions must necessarily depend upon: 



1. The affinities of the antigen for some other substance 

 intra vascular or intracellular in the organism. 



2. The nature of the reactions of the antigen with pre- 

 existing, that is to say, normal antibodies. 



3. The importance of the role which the antibodies play 

 in the life of the cells and of the cells in the organism. 



4. The nature and properties of the compounds which 

 the antigen may form with "antibodies in excess." 



Any of these reactions may present special peculiarities 



