BACILLUS ANTHRACIS. 561 
plausible explanation which can be offered, in the light of 
our present knowledge, for the solution of this 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 
Léffler. 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’ use of this 
36 
