160 BACTERIOLOGY. 



CHAPTER XXVII. 

 NON-PATHOGENIC BACTERIA. 



Material for the practical study of non-pathogenic species may 

 be obtained from air, water, soil, and other sources. The biological 

 characteristics of a few of the more common species are here given 

 to assist the student in experimental work. 



I. Bacillus Prodigiosus. 



This species is a chromogcnic, non-motile, facultative anaerobic 

 saprophyte. It produces a pigment-forming body, which becomes 

 red by the action of oxygen. The pigment gives rise to the " red 

 mould " of bread. The rods are short, often in filaments, without 

 spores. It grows rapidly upon agar-agar, or potato, at the room 

 temperature, and soon liquefies nutrient gelatin. It grows best at 

 25 degrees Centigrade. It may be obtained from the air. 



II. Bacillus Acidi Lactici. 



Bacillus acidi lactici occurs in sour milk, producing lactic acid. 

 It is a non-motile, facultative anaerobic saprophyte. It produces a 

 whitish growth on agar-agar, does not liquefy gelatin, ancl the rods 

 occur in pairs or short filaments, producing large shining polar- 

 spores. It causes milk to sour, changing its sugar into lactic acid 

 and CO 2 , and precipitates casein. It will grow at 10 degrees Cen- 

 tigrade; but, when cultivated for several generations, it loses its 

 power to produce fermentation.. 



III. Bacillis Subtilis. 



This species may be obtained from hay infusions, air, water, soil, 

 etc. It produces a grayish growth on agar, and liquefies gelatin. It 

 is a motile aerobic saprophyte, and grows rapidly at ordinary tem- 

 peratures. The rods are thick and stout, with rounded extrem- 

 ities, and provided with flagella. It produces motile spores. 



IV. Bacillus Violaceus. 



This bacillus is found in water. It is aerobic, motile, and chromo- 

 genic; grows at room temperature, and on agar produces a violet- 



