26 THEORIES OF IMMUNITY 



formation of "antibodies" and at the moment they can 

 hardly be called anything else because all we know of them 

 except in the case of arsenobenzene, is that they are recipro- 

 cally "anti." When after a preparatory treatment, the in- 

 tensity and duration of which may vary widely for different 

 antigens and different animals, the prepared animal is bled 

 and the blood serum mixed with the antigen in a test-tube, 

 reactions are seen which are not produced with the serum of a 

 normal animal and which are different according to the nature 

 of the antigen injected. 



Toxins (diphtheria, tetanus, botulism), some venins and 

 poisons of certain mushrooms cause the formation of anti- 

 bodies which neutralize the pathogenic effects of these poisons 

 without visible change. The mixture of the two liquids 

 remains clear and one can determine neutralization of the 

 "antigen" only by injecting the mixture into a susceptible 

 animal. After a sufficient preparation, a relatively very 

 small quantity of the blood serum of the treated animal is 

 able to neutralize a large number of "lethal doses" of the 

 antigen. One cubic centimeter of antitetanic serum may, 

 for example, often neutralize a thousand or even more times 

 the dose of toxin necessary to kill a guinea-pig and it is this 

 property of the antibody discovered by Behring and Kitasato 

 which E. Roux first utilized in the practical serum treatment 

 of diphtheria arid in the preventive treatment of tetanus 

 and which Calmette also used in the preparation of anti- 

 venomous serum. 



Ricin, a vegetable antigen extracted from rice, whose com- 

 position is unknown but whose effects on the organism pre- 

 sented many analogies with that of diphtheria toxin, forms 

 with its antibody an insoluble compound. When antiricin 

 serum is added to a solution of ricin a precipitate is formed 

 and if the two solutions have been mixed in suitable propor- 

 tions the supernatant fluid will contain neither ricin nor free 

 antiricin. We have been able to conclude then that a part 

 if not all the antigen and antibody are combined or fixed one 

 by the other and are contained in the precipitate and this 

 supposition has been confirmed by experiment. By sub- 

 mitting the precipitate to the action of gastric juice which 



