82 PHYSIOLOGICAL ACTIVITIES 



fermentation" of carbohydrates by bacteria. Each kind of 

 bacterium, as a rule, forms several different acids as well as 



Fig. 56.— a loaf of "salt-rising" bread. The porous structure is due to the 

 gas formed by bacilli and not by yeasts. 



other substances, though usually one is produced in much 

 larger amounts, and the kind of fermentation is named from 



Fig. 57.— Ohio Swiss cheese. The "eyes" are due to gas formed by bacteria 

 during the ripening of the cheese. 



this acid. One of the commonest of these acids is lactic. 

 The "lactic acid bacteria" form a very large and important 



