BACILLUS ANTHRACIS. 561 



plausible explanation which can be offered, in the light of 

 our present knowledge, for the solution of thib problem, 

 is the supposition that under certain natural conditions 

 unfavorable to the development of the anthrax bacillus 

 an attenuation of its virulence takes place, and then, 

 again, an increase of virulence as the condition becomes 

 more favorable a result which can be produced by arti- 

 ficial means. But whether this actually occurs we do 

 not know. 



Prophylaxis Against Anthrax Infection. Numerous 

 investigations have been undertaken with the object of 

 preventing infection from anthrax. The efforts of Pas- 

 teur to effect immunity in animals by preventive inocu- 

 lations of " attenuated virus" of the anthrax bacillus, 

 opened a new field of productive original research. Fol- 

 lowing in his wake many others have prepared methods 

 of immunization against anthrax infection; but the one 

 adopted by Pasteur, Chamberland and Roux has alone 

 been practically employed on a large scale. According 

 to these authors, two anthrax cultures of different de- 

 grees of virulence, attenuated by cultivation at 42 to 

 43 C., are used for inoculation. Vaccine No. 1 kills 

 mice, but not guinea-pigs; Vaccine No. 2 kills guinea- 

 pigs, but not rabbits, according to Koch, Gaffky, and 

 Loffler. The animals to be inoculated viz., sheep 

 and cattle are first given a subcutaneous injection 

 of one to several tenths of a cubic centimetre of 

 a four-day-old bouillon culture of Vaccine No. 1; 

 after ten to twelve days they receive a similar dose 

 of Vaccine No. 2. Prophylactic inoculations given 

 in this way have been widely employed in France, 

 Hungary, and Russia. Statistics collected by Cham- 

 berland of the results of twelve years 7 use of this 



36 



