384 BACTERIA PATHOGENIC TO MAN 



Staining. The anthrax bacillus stains readily with all the aniline 

 colors, and also by Gram's method, when not left too long in the 

 decolorizing solution. In sections good results may be obtained by 

 the employment of Gram's solution in combination with carmine, 

 but when only a few bacilli are present this method is not always reli- 

 able, as some of the bacilli are generally decolorized. 



Biology. The anthrax bacillus grows easily in a variety of nutrient 

 media at a temperature from 18 to 43 C., 37 C. being the most favor- 

 able temperature. Under 12 C. no development takes place, as a rule, 

 though by gradually accustoming the bacillus to a lower temperature 

 it may be induced to grow under these conditions. Under 14 C. and 

 above 43 C. spore formation ceases. The lower limit of growth and 

 of sporulation is of practical significance in determining the question 

 whether development can occur in the bodies of animals dead from 

 anthrax when buried at certain depths in the earth. Kitasato has 



FIG. 117 



Spores heavily stained (in specimen red). Bodies of disintegrating bacilli faintly stained 

 (in specimen blue). X 1000 diameters 



shown that at a depth of 1.5 metres the earth in July has a tempera- 

 ture of 15 C. at most, and that under these conditions a scanty sporu- 

 lation of anthrax bacilli is possible, but that at a depth of 2 metres 

 sporulation no longer occurs. The anthrax bacillus is aerobic that 

 is, its growth is considerably enhanced by the presence of oxygen 

 but it grows also under anaerobic conditions, as is shown by its growth 

 at the bottom of the line of puncture in stick cultures in solid media; 

 but under these conditions it no longer produces the peptonizing fer- 

 ment which it does with free access of air. Furthermore, the presence 

 of oxygen is absolutely necessary for the formation of spores, while 

 carbonic acid gas retards sporulation. This explains, perhaps, why 

 sporulation does not take place within the animal body either before 

 or after death. 



This bacillus grows best in neutral or slightly alkaline media. It 

 may be cultivated in infusions of meat or of various vegetables, in 



