ANTHRAX. 197 



inoculated a second time with material (deuxieme vaccin) which has 

 been less weakened. The animals are then protected against the 

 most virulent anthrax, but only for a time. From a weakened 

 culture, according to Klein, new cultures of virulent bacilli can be 

 started, and a culture that can be used as a vaccine for sheep kills a 

 guinea-pig, and then yields bacilli that are fatal to sheep. 



The virulence of the bacillus is also altered by passing the 

 bacillus through different species of animals. The bacillus of sheep 

 or cattle is fatal when re-inoculated into sheep or cattle; but if 

 inoculated in mice, the bacilli then obtained lose their virulence 

 for sheep or cattle, only a transitory illness results, and the animals 

 are protected for a time against virulent anthrax. 



Exposure to a temperature of 55 C., or treatment with *5 to 

 1 per cent, carbolic acid, deprives the bacilli of their virulence. 



Chauveau obtained a similar result by cultivating the bacillus at 

 38 or 39 C. under a pressure of eight atmospheres. The possibility 

 of mitigating the virus depends upon the species of animal ; rodents 

 cannot be rendered immune by any known anthrax vaccine. The 

 nature of the toxic products has been described in a previous chapter 

 (p. 42). 



METHODS OF STAINING THE BACILLUS ANTHRACIS. 



Cover-glass preparations of blood, etc., can be stained with a 

 watery solution of any of the aniline dyes, or with Neelsen's solution 

 and subsequent treatment with alcohol (p. 87). The preparations 

 may be dried and mounted permanently in Canada balsam, but the 

 typical appearances are best observed in freshly stained specimens 

 examined in water. 



The sheath and protoplasmic contents can be demonstrated in 

 cover-glass preparations from the 

 blood or spleen which have been 

 stained with eosin after the method 

 of Gram. 



Spores must be stained by the ^ 



special methods already described. /^^ C^ 

 The most satisfactory preparations 

 are obtained by double-staining with FIG. 98. SPORES OF BACILLUS 

 Ziehl-Neelsen solution and methy- ANTHRACIS STAINED WITH 



, , /T ^. ~ v GENTIAN VIOLET, x 1500. 



lene blue (Fig. / ). 



Tissue sections are best stained by the method of Gram, and 

 after-stained with eosin, picrocarminate of ammonia, or picro-lithium- 

 carmine. 



