176 MANUAL OF BACTERIOLOGY. 



from growth of the hog-cholera bacillus. Such pigeons 

 were found to be immune to this bacillus, which is patho- 

 genic for ordinary pigeons. 



As was stated in the last chapter, bacterial poisons may be 

 of two sorts. In one group the poisons occur chiefly within 

 the bodies of the bacteria. This group seems to contain the 

 majority of the pathogenic bacteria. Methods of protection 

 against infections caused by them will be considered here- 

 after. But an ti-endo toxins, or substances which counteract 

 intracellular or endotoxins, have not yet been satisfactorily 

 produced.* 



In the other group the poisons do not, for the most part, 

 remain in the bodies of the bacteria, but are readily diffused 

 from them into their surroundings. It is for the bacteria of 

 the latter group that antitoxins have been obtained. Its 

 most important members are the bacilH of diphtheria and 

 tetanus. Their poisons may be found in the culture-media in 

 which they have grown. The principle employed in preparing 

 antitoxins was established by Behring, who found that 

 by injecting susceptible animals with increasing amounts of 

 toxin he produced in the blood-serum of the injected animal 

 certain changes which made the serum capable of counter- 

 acting the toxin when injected into other animals. Thus, a 

 sheep treated with increasing doses of diphtheria toxin, begin- 

 ning with very small amounts, furnishes blood-serum which 

 protects other sheep or guinea-pigs or other susceptible animals 

 from- fatal doses of diphtheria toxin. In practice the bacilli 

 are cultivated in bouillon. The cultures are freed from all 

 living bacilh by filtration. The liquid filtrate contains the 

 toxin. This filtrate is injected into healthy susceptible ani- 

 mals, in increasing doses. Usually the horse is used, since 

 large quantities of blood can be drawn from this animal on 



*Kolle and Wassermann. Handbuch der pathogenen Mikroorganismen. 

 Bd. I., p. 373. Jena, 1903. 



