CHEMICAL AND HUMORAL THEORIES OF IMMUNITY 315 



facts, a wholly natural explanation of the non-recurrence 

 of virus diseases. 



Let us investigate in this direction. Why does not the 

 same bouillon culture nourish easily a second time the 

 species which has already lived in it? The failure might 

 result from one of two things: either the organism 

 removed from the bouillon the first time a substance 

 needed in its development, or else it deposited in it an 

 injurious substance. 



Pasteur and his colleagues inclined toward the first ex- 

 planation. M. Chauveau, on the contrary, favored the 

 second and supported it on two arguments of unequal 

 value. He was of the opinion, for instance, that the 

 vaccination of the foetus by the mother, that is to say, 

 the transmission of immunity through the placenta, 

 which he had often had occasion to verify in anthrax, and 

 which MM. Arloing, Cornevin and Thomas had just 

 proved for the symptomatic anthrax, was better ex- 

 plained by the introduction of an injurious substance 

 into the blood of the foetus, than by the disappearance of 

 a needed substance. The two bloods of the mother and 

 of the foetus being constantly in position to exchange 

 chemical substances, are likewise in position to lose or 

 to acquire, and there appear to be no reasons for be- 

 lieving that preference is given one over the other. 

 Another argument of M. Chauveau was worth more. 

 He called attention to the curious influence of the quan- 

 tity of virus used in inoculation. The Algerian sheep is 

 immune to doses which kill the French sheep, but, if 

 we increase the dose, we also kill the Algerian sheep. 

 If it is much diminished, the French sheep resists in its 

 turn, experiencing only an illness, from which it emerges 

 vaccinated. This is not explained by the hypothesis of 

 Pasteur. If there is lacking in the sheep an element 

 needful for the multiplication of the bacteridium, we 



