ANTHRAX GROUP 333 



tores in agar or gelatin are sometimes necessary when the organism 

 is mixed with other forms. The colonies microscopically are 

 found to consist of long chains of bacilli, which, under the low 

 power, resemble tufts of curled hair. This appearance is quite 

 characteristic, but is closely duplicated by certain soil organisms 

 of the Bacillus subtilis group. In gelatin stabs a " spiking " 

 occurs, i. e., filaments radiate from the line of puncture and give 

 the appearance of an inverted fir tree. The gelatin is liquefied 

 slowly. The growth on potato is creamy in color and rather dry 

 in consistency. Blood-serum is slowly liquefied. Milk is rendered 

 slightly acid, curdled by a lab ferment, and the casein digested. 



, 



'- 



Fig. 136. Bacillus anthracis, with spores (Frankel and Pfeiffer). 



In bouillon the organism frequently forms a pellicle which readily 

 settles to the bottom. Clouding of the medium does not 

 occur. 



Physiology. Bacillus anthracis grows best in the presence of 

 oxygen. The optimum growth temperature is about 37. It 

 will grow at temperatures as high as 45, and also at room-temper- 

 ature. The vegetative rods are easily destroyed by heat, but the 

 spores must be heated to 100 for five minutes before they are 

 certainly killed. The spores likewise exhibit great resistance 

 to desiccation. Dried upon threads, they have been known to 

 retain their vitality for years. Five per cent, phenol destroys 



