Natural immunity against toxins 339 



preliminary measure, deprives this conclusion of the degree of certainty 

 one would like to have in such a matter. On the other hand, the 

 greater susceptibility of young hedgehogs prevents us from putting 

 the immunity of the t adult in the category of natural immunity 

 properly so called. 



Analogous considerations apply in the case of the mongoose [356] 

 (Herpestes ichneumon), carefully studied by Calmette 1 , according 

 to whose researches the Antilles mongoose is not very susceptible 

 to snake venom; it readily withstands doses very large relatively 

 to its size, but its immunity is not absolute. It owes much of its 

 mastery in its fights with venomous snakes to its extraordinary 

 agility. The blood of the mongoose, mixed with venom, exhibits an 

 undoubted antitoxic power, though this is not sufficient to prevent 

 the death of susceptible animals. We have no data to enable us to 

 explain the origin of this antitoxic property, but it is probable that 

 here again we have an example of relative immunity, acquired during 

 life. Calmette points out, however, that his ichneumons came from 

 Guadeloupe, where no venomous snakes are found. We may, of 

 course, suppose that the feebly antitoxic power of the blood of these 

 mammals might be due to other snakes or to species of animals 

 whose blood possesses a certain venomous property 2 . 



We have far more exact data on the natural immunity of certain 

 mammals against toxins of microbial origin. The example most 

 thoroughly studied, one which has become, one might say, classic, is 

 that of the rat against diphtheria toxin. Since the discovery of this 

 toxin, the first well-studied bacterial poison, a discovery made by 

 Roux in collaboration with Yersin, it has been recognised that mice 

 and rats tolerate large quantities of diphtheria cultures or of their 

 filtered products. A rat resists a dose of the diphtheria poison 

 capable of killing several rabbits. To explain this great natural 

 immunity it was suggested that the antitoxic property of the 

 body fluids could be called in. It was supposed that the rat's blood 

 was, by its very nature, endowed with the power of neutralising the 



1 " Le venin des serpents," Paris, 1896, p. 43. 



2 The temporary immunity of the marmot (amongst mammals) against tetanus 

 toxin must be considered separately. According to Billinger and Donitz the marmot 

 is insusceptible to this poison during its winter sleep. But once it is awakened it 

 readily contracts tetanus. H. Meyer, Halsey and Ransom have observed the same 

 fact in hibernating bats that have been waked up. In these cases the immunity is 

 dependent on the low temperature which approximates these examples to that of the 

 natural immunity of the frog against the same toxin. 



222 



