BUTYRIC ACID FERMENTATION 109 



is rapidly liquefied ; gas development ; slight undulating colonies, as if consisting of 

 mass of felted threads. No odour. 



Agar plates and tubes A luxuriant growth with gas development and ramifica- 

 tions in medium. Odour present. 



Potato Growth extends into potato substance ; smell of alcohol. 



Milk At 37 C., after fifteen hours casein precipitated and butyric acid is formed 

 without intermediate formation of lactic acid. Coagulum eventually dissolves ; 

 before that stage the appearance is very characteristic ; there is a spongy fatty 

 layer on surface, then clear fluid, and then a white deposit The presence of this 

 organism is readily proved in almost all milk. Fill a half litre flask with milk, and 

 steam at 100 C. for half an hour. Incubate at 37 C. In less than twenty-four 

 hours the characteristic changes will occur, with strong odour of butyric acid. 

 Care must be taken that the gas pressure does not burst the flask. There is a 

 marked odour of butyric acid. Other acids present are acetic, formic, and lactic. 



Anaerobic or aerobic Facultative anaerobe. 



Non-pathogenic It has been suggested that the B. enteritidis sporogtnes of Klein 

 is a pathogenic form of this bacillus. 



2. Bacillus Butyricus (Hiippe) 



Source and habitat Milk. 



Morphology Slender rods ; 1-2 to 4 /A long, 0'5 //. thick; round ends. May 

 grow into filaments ; rods slightly bent ; 21 n long, 0'3 A* broad. 



Staining reaction Stains by Gram's method. 



Flagella ; motility Many flagella ; actively motile. 



Spore formation Oval spores at 37 C. ; mesially situated. 



Biology : cultural characters (including biochemical features'). 



Bouillon A pellicle is formed ; bouillon remains clear. No indol. 



Gelatine plates and tubes Small whitish-yellow colonies with crater-shaped 

 depression ; liquefaction ; whitish-grey wrinkled pellicle produced in liquid 

 cultures in tubes ; liquefied medium cloudy and yellowish in colour. 



Agar plates and tubes A thin yellow layer, similar to B. mesentericus. 



Potato A fawn-coloured transparent layer, sometimes wrinkled. Somewhat 

 similar to B. megatherium. 



Milk Is coagulated. Precipitated casein subsequently dissolved. Bitter taste. 

 Butyric acid produced from salts of lactic acid ; also from milk-sugar when it is 

 previously hydrated. 



Facultative anaerobe. 



Non-pathogenic. 



3. Bacillus Butyricus (Pasteur). (Vibrion Butyrique) 



Source and habitat MY, and thence to milk. 



Morphology Cylindrical rods with rounded extremities 5 3 /* to 5 /u long by 

 6 fi to '8 /i broad. Isolated or in chains ; at times in long filaments indistinctly 

 articulated. 



Staining reaction Ordinary aniline stains. 



Motility Feebly motile ; motility ceases at once in presence of free oxygen. 



Spore formation Ovoid spores. 



Biology : cultural characters (including biochemical features'). 



Bouillon Grows freely under strictly anaerobic conditions in bouillon contain- 

 ing lactate of lime. 



Agar plates and tubes In agar " shake " cultures free from oxygen the medium 

 becomes clouded in the lower portion, and is soon broken up, with copious gas 

 formation accompanied by strong smell of butyric acid. 



Gelatine plates and tubes As upon agar, but in a less degree, the medium 

 liquefying in the neighbourhood of the forming colonies. 



Anaerobic. 



Non-pathogenic. 



Several other butyric acid organisms have been isolated, of which a few notes 

 may be added : 



