Immunity in Unicellular Organisms 21 



to the conclusion that the blood of the rat contains an organic base 

 capable of killing and dissolving a considerable number of anthrax 

 bacilli. Several observers have confirmed von Behring's observation 

 and have supplemented it by the fact that the bacillus can be readily 

 accustomed to the toxic action of this serum. Thus Sawtchenko 1 , in 

 an investigation carried out in my laboratory, was able, by successive 

 cultures, to accustom the anthrax bacillus to an existence in the pure 

 serum of the rat. In this case, therefore, there has been produced a 

 real acquired immunity of a lower plant against a toxic substance of 

 animal origin. More recently Danysz has demonstrated the same thing 

 and has added several other facts which seem to throw light upon the 

 means by which the bacterium becomes adapted to the poison. He 

 has shown, in a work carried out in the Pasteur Institute 2 , that the 

 anthrax bacillus protects itself against the toxic action of the serum 

 by surrounding itself with a thick sheath composed of a kind of 

 mucus which fixes the toxin of the rat's blood and renders it 

 harmless. This same mucus, but in smaller quantity, is likewise 

 produced in a culture of the bacillus grown in ordinary broth. When 

 such a culture is freed from the contained bacilli by nitration through 

 porcelain and a little of this fluid is added to the rat's serum, this 

 latter becomes less bactericidal than is a mixture of the same serum 

 with ordinary broth. Danysz suggests that this is to be explained 

 by the presence in the filtrate of a certain quantity of the mucous 

 substance produced by the bacillus, which fixes and neutralises a 

 portion of the "rat toxin." If, in place of sowing the ordinary 

 bacillus, sensitive to this toxin, we inoculate the broth with an 

 anthrax bacillus which has previously been accustomed to the rat's 

 serum, we find that the liquid of this culture when filtered neutralises 

 a larger proportion of the toxin. Danysz concludes from this that the 

 acclimatised bacillus has acquired the property of producing more 

 mucus than does the ordinary bacillus and that, for this reason, a 

 greater quantity of this protective substance passes into the fluid of 

 the culture. 



The formation of a transparent sheath has several times been [24] 

 observed in the anthrax bacillus, notably in cases where this organism 

 happens to be in "a state of defence" against various noxious 

 influences. For example, this sheath is well developed in the 

 anthrax bacillus which invades the blood of lizards, animals which 



1 Ann. de VInst. Pasteur, Paris, 1897, t. xi, p. 872. 



2 Ann. de FInst. Pasteur, Paris, 1900, t. xiv, p. 641. 



