SUGAR IN" THE NUTRIENT MEDIUM. 149 



contains grape sugar (derived from the meat).* Ac- 

 cording to Smith all strict or facultative anaerobics 

 form acids out of sugar, the aerobics either do not 

 or they do it so slowly that the formation of the acid 

 is concealed by the parallel production of alkali. 

 Prior to a knowledge of this work we had found that 

 all tested varieties of bacteria (about sixty), which 

 are shown in the Atlas, formed more or less free 

 fixed acid in one per cent grape sugar peptone 

 bouillon (vide Table I). The formation of acid 

 may or may not be attended with visible develop- 

 ment of gas. Intense production of acid may kill 

 the cultures (for example, bacterium coli, vulgare, 

 etc.). 



In many varieties the formation of acid or decom- 

 position of sugar is intense and rapid, so that this 

 metabolism, which is effected chiefly at the expense 

 of the carbohydrates, is called fermentation. Inas- 

 much as this is attended not infrequently by the de- 

 velopment of gas in large quantity, this term also 

 seems justifiable to the laity. 



If, after the sugar is used up, the amount of acid 

 produced is insufficient to kill the bacteria, the metab- 

 olism which ensues is that common to the non-sac- 

 charine nutrient medium, the acid is gradually neu- 

 tralized, and finally an increasing alkaline reaction 

 sets in. 



Among the acids produced (apart from carbonic 

 acid, which will be considered under the heading of 

 "Production of Gas") the most important and widely 

 distributed is lactic acid. In addition we almost 



* According to Th. Smith, seventy -five per cent of commercial 

 beef contains distinct amounts of sugar (up to 0.3 per cent). 



