CHAPTER XVII. 

 BACTERIACE^E: THE SPOROGENIC AEROBES. 



The aerobic spore-forming bacilli are essentially inhabitants 

 of the soil and the fermenting organic material likely to occur 

 there. Along with a few species of this* group we shall consider 

 one pathogenic sporogenous bacterium, the anthrax bacillus, 

 which resembles them very closely except in its virulence for 

 animals and its lack of active motion, both of which may perhaps 

 justly be regarded as variations from the group type due to its 

 parasitic mode of life. 



Bacillus Mycoides. This organism is universally distributed 

 in fertile soils and also occurs in surface waters and in the air. 

 It is a large rod with rounded ends, usually growing in threads. 

 Large median spores are formed without distorting the cell. 

 It is motile but rather sluggish. Growth occurs on all ordinary 

 media. In gelatin stab-culture, thread-like processes extend 

 out on all sides from the line of puncture giving the appearance 

 of an inverted pine tree. Later the gelatin becomes entirely 

 liquefied. The organism is an important agent in the decompo- 

 sition of plant residues in the soil. It is without pathogenic 

 properties. 



Bacillus (Mesentericus) Vulgatus. This is another widely 

 distributed soil bacterium. It is commonly called the potato 

 bacillus. The cell is short and relatively thick with rounded 

 ends, actively motile, often in pairs or threads. Large spherical 

 median spores are produced without distortion of the cell. 

 These spores are very resistant to heat and germicides, sometimes 

 surviving the temperature of boiling water for several hours. 

 B. vulgatus grows well on all ordinary media. Gelatin is liquefied. 

 Milk is coagulated and then digested. On potato a wrinkled 



268 



