IMMUNITY. 329 



Roux and Vaillard found that a mixture of 

 tetanus toxin and tetanus antitoxin which was 

 wholly without effect upon healthy animals, 

 caused tetanus in animals of the same species 

 which had previously suffered from other dis- 

 eases and thereby become weakened. They 

 discovered also that healthy animals which had 

 supported inoculation with the mixture appar- 

 ently without any effect, subsequently devel- 

 oped tetanus when inoculated later with the pro- 

 ducts of other bacteria; at least part of the toxin 

 had remained in the body of the animal for 

 several days without producing any effect, but 

 also without being destroyed. 



Calmette, Phisalix and Bertrand found that 

 snake-venom, abrin and ricin are destroyed by 

 heat less easily than are the respective anti- 

 dotes found in the serum after the establish- 

 ment of a tolerance of these poisons. If a 

 mixture of one of these toxins and its antidote 

 be heated, the antidote is the first to be de- 

 stroyed, the poison remaining behind. By 

 heating such mixtures to 68-7o these ob- 

 servers demonstrated that the poisons persist 

 in spite of the treatment, and therefore can not 

 have been neutralized or destroyed by the anti- 

 dotes. On the other hand, when a mixture of 

 the diphtheria toxin and its antidotal serum is 

 heated to 68 the toxin is destroyed first and 



