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which is accomplished by a peculiar kind of micro-organism, to which 
he gave the name of levure lactique (lactic yeast). His first commu- 
nication on this subject was read to the Scientific Society of Lille, 
August, 1857, and afterwards to the French Academy in November, 
1857. Since then our knowledge of the lactic acid fermentation has 
been considerably extended through the labors of Pasteur’s students 
and still later through the work of other bacteriologists and chemists. 
For example, Boutroux (4) in 1878, in continuing the investigations 
of Pasteur on the souring of milk, arrived at the conclusion that the 
lactic acid ferment and the mycoderma aceti, which is concerned in 
the transformation of alcohol into acetic acid in vinegar making, are 
identical, but that these vary in function, depending on their general 
environment and the composition of the liquid in which they grow. 
This communication also contains a description of the lactic ferment 
and an enumeration of its morphological characteristics, which are 
beyond the scope of the present communication. He observed that 
the organism grew best in a nutrient medium containing, besides 
albuminous matter, invert-sugar or glucose. He also found that 
under these conditions the liquid can attain a maximum acidity of 
1.5 per cent lactic acid. Larger amounts of acid than this checked the 
life and growth of the organism, and hence if it is desired to convert 
all of the sugar into lactic acid the acid must be neutralized with chalk 
or zinc carbonate as fast as formed. Under proper conditions the 
lactic acid organism employed by Boutroux produces lactic acid only. 
The lactic acid fermentation of milk sugar was also investigated by 
Riche t (5), who found that when milk is kept at 40° C., it becomes 
acid and coagulates and finally attains an acidity of l.b per cent, 
which amount it never exceeds. He made the further interesting 
observation that if gastric juice be added to milk the casein is coagu- 
lated and finally dissolved, and in less than twenty-four hours the 
milk contains a larger quantity of lactic acid than otherwise would 
have been present in a week, and after four or five days as much as 4 
per cent of lactic acid was formed. He observed that while neither a 
pure solution of lactose nor gastric juice will ferment, if the two be 
mixed fermentation takes place; and that the casein of milk after it 
has been dissolved by gastric juice also ferments, yielding lactic and 
butryic acids, besides other products of fermentation. On the other 
hand the whey of milk obtained by coagulation with rennin never 
attains an acidity higher than 1.6 per cent of lactic acid, even after 
having been kept for six months. Pie found that the lactic acid 
fermentation is increased by exposing a large surface of the milk to 
the air. The activity of the ferment increases up to 44° C., remains 
constant 'between 44 and 52° C., and above 52° C. diminishes in 
activity as the temperature rises. Digestive juices and peptones 
