84 IMMUNITY AND ANAPHYLAXIS 



same way as pathogenic bacteria and it is natural that it 

 should be so, because bacteria can act only through their 

 soluble products of secretion or through bacteriolysis. 

 There is at once antitoxic immunity and anaphylactic sen- 

 sitization, active and passive. 



4. For exclusively nutritive albumins there can be no active 

 and passive immunity, but there is active and passive ana- 

 phylaxis. 



All these substances have a common property. Injections 

 of them into a normal animal in non- or slightly pathogenic 

 doses always causes a reaction of the same nature: the 

 formation of an antibody which is specific without being 

 always exclusively specific. They are all grouped under 

 the name of antigens. The substances which are formed 

 in the organism by these antigens and which possess a 

 special, if not always exclusive, affinity for the corresponding 

 antigens are called antibodies. 



In attempting to define the physicochemical properties of 

 antigens, it is recognized that they are always albumins or 

 colloids; as to antibodies it is not possible to isolate them 

 from the albumins of the serum in which they are found. 

 They should be considered as colloids or at least having 

 an action like colloidal action. 



All albumins are not "antigens." This property belongs 

 only to albumins called heterologous while homologous 

 albumins that is, belonging to the individual of the same 

 species do not produce the formation of antibodies, and 

 therefore do not produce anaphylaxis. The reaction which 

 causes the formation of antibodies and which confers immun- 

 ity alone, or both immunity and anaphylaxis, or finally 

 anaphylaxis alone, is not determined solely by the physico- 

 chemical nature of antigens since homologous albumins are, 

 from this point of view, identical with heterologous albu- 

 mins. This reaction depends upon the state of the treated 

 organism with reference to the injected antigen. 



For example, an organism strongly (actively) immun- 

 ized against tetanus or diphtheria toxin will react in the 

 same way to a second dose of one of these toxins as a normal 

 organism would react to a homologous albumin. In other 



