ENZYMES AND OTHER FERMENTS DIGESTION. 14! 



can be found in the air, especially of pastures or cowsheds. 

 Many soils also contain the organism. In no case, however, 

 is the reaction a perfectly sharp one ; along with the lactic acid 

 other products are formed, acetic acid, alcohol, formic acid, 

 carbon dioxide and hydrogen being the most common. In 

 some cases the proportion of lactic acid is relatively small. 

 The formation of lactic acid may be illustrated by a labora- 

 tory experiment. 



Ex. To 100 cc. of 20 per cent cane sugar solution add an equal volume 

 of aqueous malt extract and 10 to 15 grams of precipitated chalk. Inocu- 

 late this mixture with a culture of lactic acid bacteria and keep at a tem- 

 perature of about 40 C. for some days. The chalk is necessary to take 

 up the acid as fast as formed; without it the .fermentation soon ceases, as 

 the ferment is extremely sensitive to the action of free acid. The mixture 

 must be shaken from time to time. As the fermentation progresses the 

 slightly soluble calcium lactate begins to separate. In a good fermenta- 

 tion enough of this forms to fill the fermenting vessel with a mass of 

 crystals. These crystals are redissolved in hot water, and the solution 

 filtered. The filtrate on concentration deposits crystals of calcium lactate, 

 Ca(C3H 5 O3)2.5H 2 O, which may be collected and dried between folds of 

 filter paper. The free lactic acid may be obtained by decomposing the 

 calcium salt with sulphuric acid in the proper amount and shaking out 

 with repeated small portions of ether. The lactic acid dissolves in the 

 ether and is left when this is evaporated. Zinc oxide may be employed 

 in place of calcium carbonate to neutralize during the fermentation. In 

 this case zinc lactate forms, from which the acid may be separated by dis- 

 solving the crystals in hot water and decomposing the solution by means 

 of hydrogen sulphide. 



Several pure cultures of lactic acid bacteria can now be obtained for 

 technical use. For the rapid production of the acid Lafar recommends 

 Bacillus acidificans longissimiis. 



Pure lactic acid as prepared by fermentation is a thickish 

 liquid, with marked acid taste and but slight odor. It is 

 optically inactive, but may be resolved into active components 

 by treatment with strychnine, which crystallizes with the levo 

 modification. This common fermentation acid is employed 

 for several purposes in the industries and is now compara- 

 tively cheap since the introduction of methods of fermentation 

 with pure cultures. 



Lactic acid fermentations are concerned in many common 

 operations. In the leavening of bread along with yeast fer- 



