372 Chapter XII 



whilst the second is diphtheria in which the controls do not succumb 

 until the sixth day after injection. The effect of the anticytase 

 serum being only very transitory, it is quite natural that this should 

 manifest itself in an infection of short duration and should not do so 

 in a slow intoxication. Besides, Wassermann himself has shown that 

 in several other cases of immunity against micro-organisms (the bacilli 

 of influenza and of leprosy) the injection of his anticytase serums does 

 not interfere with the perfect resistance of the animals. But even 

 were it demonstrated that the cytases really play no part in immunity 

 against toxins, the intervention of some other similar factor could 

 always be evoked. 



The analogy between immunity against micro-organisms and that 

 against toxins may facilitate the study of the relations between the 

 latter and the antitoxic power of the body fluids. In the preceding 

 [391] chapters we have described examples in which animals possess a 

 protective power in their blood but are not refractory to the corre- 

 sponding infection ; on the other hand, we have cited cases in which 

 acquired antimicrobial immunity exists without the blood presenting 

 any appreciable protective power. The idea of measuring acquired 

 immunity against micro-organisms by the measurement of the pro- 

 tective or agglutinative power of the blood must therefore be 

 abandoned, and it is impossible to regard immunity against toxins 

 as a function of the antitoxic property of the body fluids. As we 

 have seen, animals completely refractory to tetanus, such as the 

 cayman, whose immunity does not depend on the antitetanic power of 

 the blood, develop antitoxin after the injection of toxin. A similar 

 state of affairs, but less pronounced, has been demonstrated by 

 Vaillard as occurring in the fowl. The fowl, in spite of its very 

 marked natural immunity against tetanus, produces antitetanin as the 

 result of the introduction into its body of tetanus toxin ; the rabbit, 

 on the other hand, a susceptible animal, may acquire a real immunity 

 without the development of any antitoxic power in its fluids. An 

 additional fact was noted by Vaillard 1 . He showed that the repeated 

 inoculation of tetanus spores along with a small quantity of lactic 

 acid, made below the skin of the tail of rabbits procured for them an 

 immunity against tetanus toxin, although no antitoxic property ap- 

 peared in their blood. In his experiments, one hundred volumes of 

 blood serum were found to be incapable of neutralising a single 

 minimal lethal dose of the toxin. The rabbit, however, still remains 

 1 Compt. rend. Soc. de biol., Paris, 1891, p. 464. 



