436 BACTERIA OFTEN EMPLOYED IN LABORATORY PRACTICE 



not at either end, but in the equatorial plane. The bacillus mega- 

 therium is strictly aerobic; on gelatin the colonies are kidney-shaped 

 or crescentic and granular after a few days' growth. The medium 

 is liquefied in stick cultures in a funnel-shaped manner. On agar a 

 whitish film is developed and on potatoes, a thick, smeary, grayish- 

 white or yellowish layer. 



Bacillus Prodigiosus. This "wonderful' 1 bacillus, so called on 

 account of the beautiful red pigment which it forms, is a small rod, 

 0.5 to 1 micron long, and was formerly mistaken for a coccus. The 

 rod shape is most marked in slightly acid media (best acidulated 

 with tartaric acid or boric acid). The bacillus is motile, and possesses 

 flagella, arranged on one side. It does not form spores, but can 

 resist drying out for a considerable time; it often forms yeast-like 

 involution forms. Pigment formation is best at 20 to 24 C. Gelatin 

 is liquefied rapidly. On agar the colonies are at first without color, 

 but it appears later. The pigment is only formed in the presence 

 of oxygen. The most intense color is formed on potatoes. Milk is 

 likewise stained red. Sugar is fermented by this organism. 



A considerable number of different bacilli occurring in water form 

 a red pigment, as the Bacillus ruber aquatilis, Bacillus rubefaciens, 

 Bacillus rubescens, etc. 



Bacillus Violaceus. This organism has frequently been found in 

 water. It is a motile bacillus 0.8 by 1.7 micron; it generally occurs 

 in pairs, forms oval spores, and grows at room temperature, but not 

 at 37 C. In gelatin the colonies first appear like small air-bubbles 

 in the medium. They are irregular in outline and rapidly liquefy 

 the culture soil. In stick cultures the liquefaction leads to the for- 

 mation of a funnel, at the bottom of which is a violet sediment. On 

 potatoes the pigment formed is of a dark, black violet; on agar of a 

 bright, lacquer-like violet color. Blood serum is also liquefied; 

 nitrates are reduced to nitrites. The pigment of this bacillus under- 

 goes various changes when treated with a variety of dilute acids. 

 Mineral acids change the violet to blue green, chlorine water to 

 yellow, hydrate of sodium solution to brownish yellow, ammonia to 

 bluish green. The ordinary Bacillus violaceus and a number of its 

 varieties described are absolutely non-pathogenic. Wooley, however, 

 encountered a Bacillus violaceus (var. Manilse) in the Philippine 

 Islands which appears to have caused the death of several water 

 buffaloes, and which, after being obtained in pure cultures, was very 

 pathogenic for rabbits. 



Bacillus Cyanogenus. This organism causes the blue discoloration 

 of milk. It has been known for a long time, but was not obtained in 

 pure cultures until isolated by Hiippe. It varies in size from 1 to 4 

 micra by 0.3 to 0.5 micron in thickness. It is motile and possesses a 

 number of flagella at one end. It is Gram negative and grows best at 

 room temperature, not at 37 C. It is strictly aerobic. In milk it does 

 not form acid, but alkali, and does not coagulate it. The organism 



