208 AGRICULTUEAL AND INDUSTKIAL BACTEKIOLOGY 



when kept in a warm place after baking. Commercial 

 bakers not infrequently add lactic acid to the dough to 

 insure its presence in sufficient quantities. 



So-called "salt-rising" and certain types of "sour 

 dough" bread are leavened by the action of organisms 

 belonging to the genus Bacterium. They produce small 

 quantities of lactic acid and considerable quantities of gas, 

 particularly carbon dioxide and hydrogen. They thus 

 replace yeast in forming the gas bubbles essential to the 

 leavening of the loaf. 



