268 SUSCEPTIBILITY AND IMMUNITY. 





mixture into a susceptible animal, then we must admit that this 

 neutralizing effect occurs outside of the body of the animal, as has 

 been generally assumed. 



The experiments of Vaillard are also opposed to*Buchner's view. 

 He reports that in a rabbit immunized against tetanus, " a vohfme of 

 blood equal to the total, amount which circulates in its body may be 

 withdrawn without diminishing, in an -appreciable manner, the anti- 

 toxic power of its serum. Therefore the antitoxin must be repro- 

 duced as fast as it is withdrawn." The author from whom we have 

 just quoted (Roux) also reports the resujts of experiments which 

 show that the antitoxic value of the serum of a rabbit immunized 

 against tetanus does not bear a direct relation to the quantity of the 

 tetanus toxin- introduced, but depends also upon the method adopted. 

 W^ien a few large doses are given the result is far lesg favorable than 

 that obtained by giving the same amount in repeated small doses. 

 The serum of an animal immunized by thirty-three small doses was 

 found to neutralize, in vitro, 150 parts*of toxin, while that of an 

 animal which received the same amount in nine* doses only neutral- 

 ized 25 parts of the same toxin. On the other hand we have experi- 

 ments which indicate that the supposed neutralization of a toxin by 

 an antitoxin in vitro is not really a chemical neutralization. Thus 

 Buchner found in his experiments with the tetanus toxin and Anti- 

 toxin, in a dry powder, that when mixed in a certain proportion and 

 injected into white mice no tetanic symptoms were induced. But the 

 same mixture gave rise to distinct tetanic symptoms in guinea-pigs, 

 showing'that the inference that the toxin had been neutralized in 

 vitro, based upon the experiment on mice, would have been a mis- 

 take. And certain observations made by Roux and Vaillard seem 

 to give support to the view that neutralization does not occur in 

 vitro, but that the result depends upon some physiological reaction 

 induced by the antitoxin within the body of the living animal. These 

 bacteriologists found that when the antitoxin was apparently in ex- 

 cess, tetanic symptoms could* be induced in susceptible animals if 

 they had been in any way exhausted prior to the injection of the 

 mixture of toxin -and antitoxin; and that the same result followed 

 when their resisting power had been reduced by injecting into them 

 at the same time filtered cultures of other bacteria. 



In this connection the results reported by Calmette, Phisalix, 

 and Bertrand are of interest. These investigators found that when 

 the antitoxin of snake-poison was mixed with this venom in a pro- 

 portion which neutralized its toxic properties, as shown by experi- 

 mental inoculations, and the mixture then heated to 70 C., by which 



