354 AGEICULTUEAL AND INDUSTRIAL BACTEEIOLOGY 



the same diameter. The vegetative rods readily stain by 

 the aniline dyes and are Gram-positive. 



The organism culturally and morphologically very closely 

 resembles the nonpathogenic and saprophytic species of 

 the genus Bacillus as Bacillus suhtilis and Bacillus 

 mycoides. 



Culture. — The Bacillus anthracis can readily be secured 

 in pure culture from the blood or internal organs, particu- 

 larly the spleen or liver, of infected animals. The colonies 

 on gelatin or agar, when observed microscopically under the 

 low power, are seen to consist of long chains of bacilli which 

 resemble bunches of curled hair. This appearance is quite 

 characteristic, but is not very unlike that observed in cul- 

 tures of some of the saprophytic bacteria. In gelatin stabs 

 filaments develop from the sides, giving rise to a character- 

 istic spiking. . The gelatin is slowly liquefied. Milk is first 

 rendered slightly acid, then curdled and the casein finally 

 digested. In broth a pellicle is developed which readily 

 settles to the bottom and the medium is not usually clouded. 



Physiology. — The organism is aerobic and facultative 

 anaerobic. It grows best at blood heat, although growth 

 may be secured at room temperatures. The maximum 

 growth temperature is about 45° c. The rods are destroyed 

 by heat, but the spores are more resistant, requiring a tem- 

 perature approximately that of boiling water for some min- 

 utes. . The latter are also very resistant to drying and have 

 been kept alive for years dried in soil or upon threads. They 

 are among the most resistant of the spores of the patho- 

 genic bacteria. "When pastures, therefore, have been 

 infected with this organism, they may remain capable of 

 transmitting the disease for a considerable period of years. 

 Gelatin is digested. 



Pathogenesis — The organism is remarkably patho- 

 genic for many of the laboratory animals. Mice are par- 

 ticularly susceptible, guinea pigs hardly less so, rabbits are 



