BUTY-RIC ACID BACTERIA. 129 



According to Fitz the spores of butyric acid bacteria can 

 withstand the temperature of boiling water for a length of 

 time, naturally dependent, as in all cases, on their condition 

 and on the nature of the substratum ; Fitz gives three to 

 twenty minutes as limits. They can, however, be killed at 

 a lower temperature if maintained long enough ; thus they 

 are killed by being heated for six hours at 90 C. in a solution 

 of grape-sugar ; but in glycerine, at the same temperature, 

 for a period varying from six to eleven hours. 



Hueppe has likewise described a species (Bac. butyricus) 

 found in milk, and occurring in the same forms as the species 

 discovered by Prazmowski, but it proved much less sensitive 

 to oxygen, and must, therefore, be classed as an aerobe. This 

 species does not, however, form butyric acid from carbo- 

 hydrates, but from albuminoids. 



Another aerobic species, Bac. booco- 

 pricus, was detected by Emmerling in 

 cow dung. It forms short rods, and is 

 characterised by not liquefying gelatine, 

 and by converting glycerine into butyric 

 acid. 



Gruber found three well-defined 

 species associated under the name of 

 Clostridium butyricum, two of which are 

 exclusively anaerobic. One of the latter 

 species consists of straight or. slightly- 

 curved rods, which become spindle- or barrel-shaped during 

 the formation of spores. In nutrient gelatine it forms 

 colonies which, when seen in reflected light, appear brownish- 

 black or black. The second species consists of strongly- 

 curved vegetative rods, at the end of which spores appear ; 

 it forms yellowish or yellowish-brown colonies. The third 

 species is also capable of growth and of causing fermentation 

 in the absence of oxygen ; its development is, however, 

 decidedly assisted by the presence of oxygen, and it is only 

 then able to produce spores. The vegetative rods are cylin- 

 drical ; with the formation of spores the rods become spindle- 

 shaped, and in the centre of the spindle the large spore is 

 formed. The colonies in nutrient gelatine are yellowish. 



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