MICROBES, OB BACTERIA. 105 



juice of beetroots, carrots, and onions, and in liquids 

 containing sugar and nitrogenous substances. It is 

 probably produced by the same ferment which causes 

 the ropiness of wine (Fig. 55), and the liquid assumes 

 a viscous or oily appearance. 



Pasteur states that this microbe acts on the glucose 

 and transforms it into gum or dextrine, into mannite 

 and carbonic acid. The lactic and butyric fermenta- 

 tions, which are often simultaneously produced in 

 saccharine liquids, are due to distinct microbes. 



V. THE MICROBE OF LACTIC FERMENTATION. 



The sugar contained in milk, as well as grape 

 sugar, can be transformed into lactic acid. This 

 transformation is always caused by the presence of 

 a ferment with which Pasteur has made us ac- 

 quainted. It had been previously supposed that milk 

 turned sour spontaneously when it was allowed to 

 stand for some days. In this case, as we know, the 

 milk curdles, and the clear liquid which separates 

 from the curd is called whey. In 1780, Scheele, the 

 celebrated Swedish chemist, extracted lactic acid from 

 whey. The same acid is also found in sour-crout; 

 in the sour water of starch ; in baker's yeast ; in water 

 in which peas, beans, or rice have been boiled, and then 

 suffered to ferment ; and, finally, in the juice of beet- 

 root which has passed through viscous and alcoholic 



