§ IX.] Lactic acid-fermentation. 93 



and water ■without any sensible development of gas. The culti- 

 vation of Leuconostoc in solution of cane-sugar soon resulted in 

 the splitting (inversion) of the sugar into glucose and laevulose, 

 and for this reason it is so highly detrimental to the fabrication 

 of cane-sugar ; the sugar then disappears as in the first experi- 

 ment, the glucose first, and about 40-45 per cent, of the sugar 

 which disappears is expended in the formation of the Leuconostoc. 



A similar formation of mucilage to that of the viscous 

 fermentation of saccharine solutions, is seen in the ropiness 

 of beer and wine, in which condition they are capable of 

 being drawn out into filaments. These phenomena also are 

 accompanied, or doubtless caused, by the formation of Micro- 

 cocci united together in rows, and the slime may very well have 

 the same origin and morphological significance as the jelly of 

 Leuconostoc. It may be observed in passing that other so- 

 called ailments of beer and wines are caused by Bacteria, but 

 we cannot enter into any further description of them here'. 



5. The old method of inducing ordinary lactic acid fermen- 

 tation (25, 45) of the different kinds of sugar is by adding sour 

 milk or cheese to a fermentable solution and keeping it exposed 

 to the air at a temperature of 40-50° C. Calcium carbonate 

 or zinc-white must also be added in order to throw down the 

 lactic acid as it is disengaged, because the fermentation ceases 

 as soon as the acid content of the fluid exceeds a certain 

 amount. 



Pasteur first showed that a particular Bacterium, and others 

 perhaps along with it, was introduced with the cheese or sour 

 milk, and that it vegetates in the fluid, especially in the sediment 

 at the bottom, and acts as a ferment. It appears in the form 

 of minute cylindrical cells, which immediately after division are 

 scarcely half as long again as they are broad, and average 0-5 ju 

 in thickness. After each division they usually soon separate 

 from one another, rarely remaining united, and forming short 



' See Pasteur, Etudes snr le vin, Paris, 1866, and Etudes sur la biire, 

 Paris, 1872. 



