Artificial immunity against toxins 345 



animals vaccinated against these vegetable poisons, which, by theii* 

 nature, approximate to the microbial toxins, develop in their blood 

 a most marked antitoxic property. 



Some years later, the discovery of antitoxins was extended to 

 snake venoms, poisons of animal origin which, like the vegetable 

 poisons studied by Ehrlich, present a chemical composition analogous 

 to that of the microbial toxins. Phisalix and Bertrand^ and Calmette^, 

 working independently, discovered methods of vaccination against 

 snake venom and were able to demonstrate the existence of an 

 antitoxic power of the blood in immunised animals. 



The works above briefly referred to gave us the fundamental basis 

 of our present knowledge on acquired immunity against toxins. 



It would be very interesting to be able to determine whether the 

 lower animals can be vaccinated against the toxic substances to which 

 they are susceptible. Unfortunately in the study of this problem 

 we encounter very great difficulties. Making use of various methods 

 I have often tried to solve it. The crayfish is susceptible to snake 

 venom and to the ichthyotoxin of eel's serum, and I have tried at 

 various times to vaccinate it against these poisons. The results, 

 however, were so inconstant and even contradictory that I was 

 unable to draw any definite conclusion from them. 



It is, indeed, very difficult to vaccinate the lower vertebrata against 

 poisons. Several attempts have been made in my laboratory to 

 immunise frogs against tetanus toxin, but without success. Calmette 

 and Delearde^ obtained the best results with abrin. They succeeded 

 in vaccinating frogs — which are not very susceptible to this vegetable 

 toxin, though they are far from presenting a real natural immunity— 

 against doses which are absolutely fatal for the control animals. These 

 observers, however, had to proceed very cautiously, and they allowed 

 a very long interval between each injection of abrin. The blood of 

 their vaccinated frogs not only did not prove to be antitoxic against [363] 

 abrin, when injected into mice, but for long retained sufficient of this 

 toxin to poison normal mice. This experiment certainly tells against 

 the hypothesis that the acquired immunity of frogs is due to the 

 development of a specific antitoxic power in their body fluids, but it 

 does not settle the question definitely since it may be objected that 



^ Compt. rend. Soc. de biol., Paris, 1894, p. 111. 



2 Compt. rend. Soc. de biol., Paris, 1894, pp. 120, 204. [Cf. also Fraser, Brit Med. 

 Journ., London, 1895, Vol. i, p. 1309 and ii, p. 416; Nature, London, 1896, Vol Liii, 

 p. 571.] 



3 Ann. de I' Inst. Pasteur, Paris, 1896, t. x, p. 683. 



