208 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



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 7 ' 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. 



