126 MICRO-ORGANISMS AND FERMENTATION. 



which are able to live without air (" vibrions butyriques "). 

 This spontaneous butyric acid fermentation takes place most 

 vigorously at 35-40 C. Starch, glycerine, dextrin, cane- 

 sugar, maltose, lactose, and dextrose are likewise decom- 

 posed by the butyric acid ferments, and such fermentations 

 a/re of frequent occurrence, as the bacteria belonging to this 

 group are very widely distributed in nature. In order to induce 

 a, butyric acid fermentation, Fitz recommends using a mixture 

 of 2 litres of water, 100 grammes of potato-starch or dextrin, 

 1 gramme of ammonium chloride, the ordinary nutrient salts, 

 and 50 grammes of chalk ; this mixture is to be maintained 

 .at 40 C. Bourquelot recommends exposing slices of raw 

 potatoes, standing in water for two or three days at a tem- 

 perature of 25-30 C. (a temperature of 39 C. is more 

 favourable). 



A convenient process for assisting the growth of butyric 

 acid organisms is given by Beijerinck as follows : 5 per cent. 

 of finely ground fibrin is added to a 5 per cent, solution of 

 grape sugar. After vigorous boiling, it is inoculated with 

 garden soil, and immediately placed in an incubator at 35 C. 

 The fermentation will set in within a day or two. The 

 liquor is then neutralised with soda solution. A growth is 

 thus obtained of Beijerinck's Granulobacter saccharo-butyricum, 

 the majority of other bacteria being destroyed by boiling, 

 or else checked by the butyric acid fermentation. If, instead 

 of grape-sugar, cane-sugar is used together with 3 per cent, 

 of calcium carbonate, 0-05 per cent, of sodium phosphate, 

 0-05 per cent, of magnesium phosphate, and 0-05 per cent, of 

 potassium chloride, the Clostridium form develops in the 

 liquor. Botkin's process is also worthy of mention ; it consists 

 simply in heating milk in closed flasks in a current of steam 

 for half an hour, and then maintaining it at 35 C. 



The most important products of the butyric acid ferment- 

 ation are butyric acid, carbon dioxide, and hydrogen. 



In the saccharine mashes of breweries, distilleries, and 

 pressed-yeast factories, species of butyric acid bacteria always 

 occur, and if the mashes are maintained for a lengthened 

 period at certain temperatures, they develop very rapidly, 

 and exercise a retarding influence on the alcoholic ferments. 



