174 MANUAL OF BACTERIOLOGY. 



Substances which produce effects in animals similar to the 

 bacterial poisons may be extracted from certain plants, 

 notably abrin, which is derived from the jequirity bean, and 

 ricin, which comes from the castor-oil bean. The venom 

 of poisonous snakes, which is elaborated by the epithelial 

 cells of certain glands, also acts in much the same manner. 



Bacterial poisons are of two principal sorts : ( i ) Some- 

 times they appear to be formed as excretions from the bac- 

 teria. They then occur in solution in liquid cultures, and 

 they may be separated from the bacteria by filtration. 

 The toxins of diphtheria and tetanus are typical examples. 

 (2) The poisons of most bacteria occur chiefly in the bodies 

 of the bacterial cells. Such toxins are called intracellular. 

 Those of typhoid fever and cholera are examples. Precisely 

 how intracellular toxins are set free in the body of an in- 

 fected animal is not clearly understood. It is, however, 

 known that many of the bacteria in an infected individual 

 are dead and disintegrated. The theories concerning toxins 

 are also considered in the next chapter. 



Sometimes the results of the injection of excessively 

 small doses of a toxin are so tremendous as to have given 

 rise to the suggestion that the toxins may be allied to the 

 ferments, like pepsin and trypsin, in their nature. 



Owing to the instability of the toxins it has not been 

 possible to isolate them in a state of purity so as to deter- 

 mine their exact chemical character. They have, never- 

 theless, been obtained in some cases in an extremely con- 

 centrated form. Brieger and Conn obtained a toxin from 

 tetanus bacilli of which .00000005 gram killed a mouse 

 weighing 15 grams. Roux and Yersin obtained a toxin 

 from diphtheria bacilli of which .00005 gram was capable of 

 killing a guinea-pig. These figures indicate a capability 

 for poisoning that is simply inconceivable. Such proper- 

 ties permit bacteria growing in a comparatively limited area 

 to manifest their evil effects at remote parts of the body. 



