126 APPLIED BACTERIOLOGY 



rabbit could be used to prevent tbe progress of this disease 

 in animals already suffering from it. 



It was found by Ehrlich in tbe case of tbe vegetable 

 albuminoid poisons, ricin (from Ricinus communis) and 

 abrin (from Abrua precatoris), and in tbe case of serpent 

 venom by Fraser and Calmette, tbat tbe serum of animals 

 immunised against tbese substances conferred a protective 

 effect wben injected with tbese toxins into other animals. 

 Ehrlich found that the serum of a' mouse which had been 

 immunised by feeding with very minute but gradually 

 increasing doses of ricin had tbe power of protecting 

 another mouse against as much as forty times the lethal 

 dose of that poison. 



Tbe greatest advance in this direction was made by 

 Behring, Kitasato, Tizzoni, and others, whose experimental 

 researches showed that by repeated injections of animals 

 with small and at first weakened but gradually increasing 

 and non-virulent doses of either the living culture or the 

 specific toxins a state of gradually increasing resistance is 

 acquired by these animals against these diseases, and that 

 this resistance is proportionate to tbe amount of antecedent 

 injections; further, that as the resistance increases the 

 blood attains an immunising power in increasing propor- 

 tion, not only as regards the subject from which the blood 

 is derived, but also as regards a new subject ; that is to say 

 that the formation and presence of these anti-bodies become 

 not only increasingly marked in the animal which is being 

 immunised, but if injected into a fresh animal they are 

 capable of furnishing this latter with a proportionate 

 degree of resistance against subsequent infection. They 

 have further shown that the immunising power of such 

 blood serum comes into action even after infection has 

 already taken place, that is to say, the blood serum has a 

 curative therapeutic action. 



