M. Pasteur on Fermentation. 123 
the soluble state to serve as food for the recent globules; and 
thus this fermentation continues for a long time. 
The nitrogen of the yeast diminishes during fermentation from 
two reasons :—first, because the yeast increases in weight during 
- fermentation by assimilating the elements of sugar, which con- 
tains no nitrogen; secondly, in consequence of the solubility of 
certain nitrogenized principles of the yeast. 
In all alcoholic fermentation, part of the sugar becomes fixed 
on the yeast in the form of cellulose. When the yeast is formed 
in amedium consisting of pure sugar, of phosphates, and of an 
ammoniacal salt, it is clear that the cellulose is formed from the 
elements of the sugar, and that the ammonia combines with 
another part of the sugar to form the soluble and insoluble albu- 
minous matters in the globules. 
Are the phenomena analogous in the case in which sugar 
ferments in the presence of alouminous substances? Hxperi- 
ment proves that there is more cellulose in the yeast after than 
before the fermentation ; so that it is very probable, if not certain, 
that all the cellulose of the yeast-globules is formed from the 
elements of sugar. But, besides the formation of cellulose, a per- 
ceptible quantity of sugar doubtless becomes assimilated by the 
yeast; for the weight of the yeast taken, added to the weight 
of the cellulose fixed during ‘fermentation, does not equal the 
total weight of the yeast and of its soluble part, such as is found 
when the fermentation is terminated. 
The weight of the cellulose increases considerably during fer- 
mentation, which furnishes a further proof of the vitality of the 
yeast during this act. 
In every alcoholic fermentation, part of the sugar becomes 
assimilated to the yeast in the form of fatty matter. If solution 
of pure sugar be mixed with an aqueous extract of yeast which 
has been repeatedly extracted by alcohol and ether, and also with 
an imponderable weight of fresh globules, a few grammes of 
yeast are obtained containing one to two per cent. of its weight of 
fatty bodies, which are readily saponifiable, forming crystallizable 
fatty acids. This fat is formed from the elements of sugar; for 
yeast prepared in a mixture of water, sugar, ammonia, and phos- 
phates also forms fatty matter. 
Permanent Vitality of Yeast.—When yeast is mixed with a 
proportionally small quantity of sugar, after the latter has been 
decomposed, the activity of the yeast continues, but is turned 
upon its own tissues with an extraordinary energy and rapidity ; 
a weight of alcohol and carbonic acid is thus obtained, exceeding 
that which the sugar could yield. Under these conditions the 
following facts are observed :— 
lst. The action of the yeast is at first exerted on the sugar. 
