BUTYRIC FERMENTATIONS 783 



cheese, in meals of various cereals, and in soil and dung of farm 

 animals. 



The organisms capable of causing butyric fermentation are 

 long, cylindrical bacilli, which become spindle-shaped (4, Fig. 

 262) when spore-formation ij completed. They are all 

 anaerobic and furnish some of the best examples of this class 

 of bacteria. 



Within their cell-walls, or in the protoplasm, is stored up a 

 substance which resembles starch in that it becomes a violet or 

 purple colour when treated with a solution of iodine. 



The spores of all these organisms are highly resistant to 

 heat, and will sometimes retain their germinating power after 

 being subjected to the action of steam for an hour and a 

 half. 



When grown under anaerobic conditions in nutrient media 

 containing dextrose, cane-sugar, starch, or maltose, all the species 

 produce butyric acid, as well as lactic acid and considerable 

 amounts of the gases carbon dioxide and hydrogen. Milk-sugar 

 in certain cases is fermented with the production of butyric 

 acid alone, but with this exception, when carbohydrates are 

 fermented by these organisms, the production of butyric acid 

 is always accompanied by the formation of lactic acid, and 

 in some instances a larger amount of lactic acid is produced 

 than butyric. 



In ordinary fermentation of milk, the anaerobic conditions 

 necessary for the growth of any butyric organisms it may con- 

 tain are only attained after the aerobic lactic bacteria have 

 exhausted the liquid of free oxygen and given rise to lactic 

 acid. When calcium carbonate is added to milk undergoing 

 lactic fermentation, the calcium lactate formed is afterwards 

 readily changed by the butyric organisms present into calcium 

 butyrate with the simultaneous production of considerable 

 quantities of carbon dioxide and hydrogen. 



