M. Pasteur on Fermentation. 121 
‘remain more than two or three days ; for it loses weight in vacuo, 
even at the ordinary temperature, when free from water. The 
glycerine is then weighed. 
Using a very small quantity of yeast to produce the fermenta- 
tion, Pasteur finds that the weight of succinic acid obtained 
exceeds the total weight of the soluble matters contained in the 
yeast. The same is the case with the glycerine, as compared 
with that of the yeast. 
Glycerine, succinic acid, alcohol, and carbonic acid are not the 
only products of fermentation. The yeast assimilates something 
from the sugar: in one experiment 100 grms. of sugar gave up 
1} grm. to the yeast; doubtless the cellulose of the new glo- 
bules produced in the fermentation forms part of this increase. 
The equation 
Coe OM 2 CH O24 C0 
by which the alcoholic fermentation was formerly expressed, 
does not exactly represent the change. The quantity of car- 
bonic acid formed is less than that required by the equation. 
Hence a certain quantity of sugar disappears without being 
accounted for. 
Pasteur assumes that this portion of sugar is resolved into 
succinic acid, glycerine, and carbonic acid, and he represents 
the change by the equation 
49(C??H" OM) +109 HO=12(C®H® 08) +. 72(C°H8 O°) + 60CO2, 
. Succinic acid. Glycerine. 
Succinic acid and glycerine are constant and necessary products 
of alcoholic fermentation. 
Lactic acid is an accidental production of the fermentation. 
Whenever it occurs (and it is very rare), the yeast must have 
contained some lactic ferment. Hach of the ferments effects its 
usual transformation, and then the fermented liquid contains, 
besides succinic acid and glycerine, lactic acid and mannite, as 
well as a new acid. 
In the second part of his research the author examines what 
becomes of the yeast in the fermentation. He shows that the 
nitrogen of the yeast is never changed into ammonia during 
alcoholic fermentation. Far from forming ammonia, that sub- 
stance disappears; for yeast is formed in a mixture of sugar, an 
ammoniacal salt, and phosphates. 
The globules of yeast are formed of small vesicles with elastic 
sides, full of a liquid containing a soft substance more or less 
granular and vascular. This is usually near the side; but in 
proportion as the globule becomes older, it tends towards the 
middle of the cell. 
The globules are reproduced by means of gemmation, as M,. 
