TETANUS TOXIN NEUTRALIZED BY BRAIN SUBSTANCE. 357 



their correctness, but on the basis of further experiments made by 

 Marie, Metchnikoff was led to another interpretation of the results. 

 Marie found that when poison and brain substance were injected 

 separately, even large amounts of brain substance did not exert 

 any protection. Metchnikoff, therefore, did not believe in any neu- 

 tralization of poison by the brain substanc in vitro. He saw the 

 cause of the apparent neutralization in mixtures of tetanus poison 

 and brain substance in the leucocyte-attracting power of the brain 

 substance injected with the poison. According to him the leuco- 

 cytes were the agents which destroyed the poison, and the brain 

 substance only the means for attracting these. 



It is hardly within my province to subject these experiments 

 to a thorough criticism; that must be left to those directly interested. 

 I should, however, like to mention two points which appear to me 

 not to be sufficiently regarded. First, it must be remembered that 

 with a dissolved antitoxin the success in neutralization on mixing 

 antitoxin and poison in vitro is considerably higher than the thera- 

 peutic success which the same dose attains in an animal. In the 

 above experiments there is added to this the fact that we are not 

 dealing with a dissolved antitoxin. On the contrary, the poison- 

 neutralizing power is exerted by a mass which, from experience, we 

 know is absorbed with great difficulty. 



Subsequently v. Behring, as a result of his combining experi- 

 ments with brain substance, expressed doubts as to the correctness 

 of Wassermann's explanation, without, however, positively taking 

 either one side or the other. Basing his reasons on the experiments 

 of Kitashima, v. Behring 1 stated his views as follows: 



"If an emulsion of fresh brain substance from a guinea-pig is 

 mixed with a certain dose of tetanus poison, a dose whose power is 

 exactly known, it will be found that with small amounts the poison 

 will completely lose its poisonous property; with larger amounts 

 there is a distinct decrease of this property. One would now sup- 

 pose that large amounts of poison, whose poisonous property has 

 been decreased by means of brain emulsion, would require less anti- 

 toxin for their neutralization than before the addition of the brain 

 emulsion. But this is by no means always the case. In the experi- 

 ment 



1 v. Behring, Allgemeine Therapie der Infections-Krankheiten, Part I, 

 p. 1033. 



