MICROBES, OR BACTERIA. 105 
juice of bectroots, 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. Tae Microspe 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 spontancously 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 
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