266 Chapter IX 



long, spoken of as preventive substances. They are so termed in 

 the early papers of Jules Bordet treating upon this question. The 

 explanation of this designation is that, for a series of years, the 

 presence of the fixatives was revealed chiefly by the preventive or 

 protective property of the media which contained them. 



To gain a clear conception of this protective property, which 

 occupies so important a place in the study of acquired immunity, 

 we must go back to an epoch in our science when it was sought 

 to prove that the fluids of the body played a part in the production 

 of immunity. Shortly after the earliest researches on the bacteri- 

 cidal power of the blood had been made, the idea of applying the 

 results obtained in this direction to the production of immunity in 

 animals by means of injections of blood occurred. The first step in 

 this direction was taken by Richet and H^ricourt^, who succeeded 

 in vaccinating rabbits against a variety of staphylococcus by means 

 of defibrinated dog's blood. The dog is naturally refractory against 

 this organism, and the blood of a normal dog exercised a certain 

 vaccinal or protective influence on rabbits inoculated with the staphy- 

 lococcus. But this action was much more marked when Richet and 

 [280] Hericourt employed the defibrinated blood of dogs which had pre- 

 viously received inoculations of the staphylococcus. Shortly after 

 this observation, von Behring^ made his discovery of antitoxins 

 in the blood serum of animals immunised against tetanus and 

 diphtheria toxins. In collaboration with Kitasato he demonstrated 

 that the serum of these animals, when injected into normal animals, 

 protected them against intoxication by the poisons of diphtheria 

 and tetanus. This great discovery, which has been confirmed on 

 all sides and extended to other poisons, gave rise to the view 

 that a serum exerting any protective power depends solely on its 

 property of impairing the action of the toxins. A more careful 

 study of the phenomena which appear under the influence of the 

 serums has, however, demonstrated the inaccuracy of this view. 

 I was able to furnish the proofs that the blood serum of rabbits 

 vaccinated against the micro-organism of the Gentilly pneumo- 

 enteritis prevented normal rabbits from contracting a fatal infection. 

 Nevertheless, the serum exerted no influence on the toxin of this 



* Compt. rend. Acad. d. Sc, Paris, 1888, t. cvii, p. 750. 



2 Behring u. Kitasato, Deutsche med. TVchnschr., Leipzig, 1890, S. 1113. 



3 Ann.de VInst. Pasteur, Paris, 1892, t. vi, p. 299. 



