356 SUSCEPTIBILITY AND IMMUNITY. 



in the body of the immune animal which neutralizes the toxic 

 products of the pathogenic microorganism. How the presence of 

 these toxic products in the first instance brings about the formation 

 of an " antitoxine " by which they are neutralized is still a mystery ; 

 but that such a substance is formed appears to be proved by the re- 

 cent experiments of Ogata, Behring and Kitasato, Tizzoni and Cat- 

 tani, G. and F. Klemperer, and others. 



Ogata and Jasuhara, in a series of experiments made in the Hy- 

 gienic Institute at Tokio (1890), discovered the important fact that 

 the blood of an animal immune against anthrax contains some sub- 

 stance which neutralizes the toxic products of the anthrax bacillus. 

 When cultures were made in the blood of dogs, frogs, or of white 

 rats, which animals have a natural immunity against anthrax, they 

 were found not to kill mice inoculated with them. Further experi- 

 ments showed that mice inoculated with virulent anthrax cultures 

 did not succumb to anthrax septicaemia if they received at the same 

 time a subcutaneous injection of a small quantity of the blood of an 

 immune animal. So small a dose as one drop of frog's blood or one- 

 half drop of dog's blood proved to be sufficient to protect a mouse 

 from the fatal effect of an anthrax inoculation. And the protective 

 inoculation was effective when made as long as seventy-two hours 

 before or five hours after infection with an anthrax culture. Fur- 

 ther, it was found that mice which had survived anthrax infection as 

 a result of this treatment were immune at a later date (after several 

 weeks) when inoculated with a virulent culture of the anthrax 

 bacillus. 



Behring and Kitasato have obtained similar results in their ex- 

 periments upon tetanus and diphtheria, and have shown that the 

 blood of an immune animal, added to virulent cultures before in- 

 oculation into susceptible animals, neutralizes the pathogenic power 

 of these cultures. 



They have shown by experiment that the blood of a rabbit which 

 has an acquired immunity against tetanus, mixed with the virulent 

 filtrate from a culture of the tetanus bacillus, neutralizes its toxic 

 power. One cubic centimetre of this filtrate was mixed with five 

 cubic centimetres of serum from the blood of an immune rabbit and 

 allowed to stand for twenty-four hours ; 0. 2 cubic centimetre of this 

 injected into a mouse was without effect, while 0.0001 cubic centi- 

 metre of the filtrate without such admixture was infallibly fatal to 

 mice. The mice inoculated with this mixture remained immune for 

 forty to fifty days, after which they gradually lost their immunity. 

 The blood or serum from an immune rabbit, when preserved in a 

 dark, cool place, retained its power of neutralizing the tetanus tox- 

 albumin for about a week, after which time it gradually lost this 



