BUTYRIC ACID BACTERIA 291 



Many of the organisms which give butyric acid when 

 breaking down proteins are aerobic. 



(a) Belonging to this class is Bacillus butyricus, Hueppe, an 

 aerobic bacterium occasionally present in milk, and said to be 

 able to produce butyric acid from milk-sugar after this compound 

 has been hydrolysed by other organisms. 



It is a rod-shaped bacillus 8 to 10 /a, long, i to 1.2 IL broad ; 

 stains by Gram's method and has large oval spores. 



Gelatine. The colonies are yellowish-white ; liquefying stab- 

 cultures soon show deep funnel-shaped liquefied portions. 



Agar. Yellowish-white slimy colonies, rounded and slightly 

 elevated. 



Potato. A slimy yellowish-brown growth. 



Milk. Coagulated and rendered alkaline, casein peptonized ; 

 neither gas nor indole are produced, but a small amount of 

 H 2 S is formed. 



(If) In this group should be included Bacillus vulgatus (p. 126) 

 and probably other putrefactive aerobic soil bacteria, though the 

 amount of butyric acid which they produce is small. 



(c) Emmerling isolated an aerobic bacillus (Bacillus boocop 

 ricus) from cow dung which formed butyric acid from glycerine ; 

 gelatine was not liquefied by it. 



