July 30, 1870.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
83 
yeast fungus, the number of active yeast-cells is 
sometimes increased a thousandfold and more, while 
the amount of nitrogenous substance in the solu¬ 
tion decreases. During the fermentation of a pure 
sugar solution mixed with yeast, the liquid extracts 
some nitrogenous material from the yeast. In this 
way the efficacy of the yeast is reduced, and when a 
further quantity of sugar solution is added, less sugar 
is decomposed. I have found that if the yeast remain¬ 
ing after fermentation of sugar solution be washed 
with water before adding it to fresh sugar solution, 
it ceases to produce fermentation after this has been 
done twice. When it is not washed each time, it 
causes very slight fermentation in the fifth quantity 
of sugar, but is then exhausted. 
Consequently, in regard to the formation and mul¬ 
tiplication of yeast-cells, there is a difference between 
the fermentation of sugar solution with yeast and 
the fermentation of saccharine solutions containing 
nitrogenous material applicable as food for the yeast 
fungus. Pasteur’s statement, that in both cases 
there is an equal production of yeast, is destitute of 
any foundation in fact. 
Like Pasteur, I have foimd that when 1000 c. c. of 
a 10 per cent, sugar solution is mixed with 15 or 20 
c. c. of moist yeast, containing 31 to 5 grm. of dry 
substance, the weight of the yeast remaining after 
the fermentation is less than that of the fresh yeast 
taken. In this case the fermentation is very rapid 
and violent, the liquid becoming clear within three 
or four days. So long as the turbidity continues, 
this may be regarded as a certain indication that 
fermentation is still going on. 
My experiments further confirm Pasteur’s observa¬ 
tion, that when sugar solution is mixed with less 
than the above proportion of yeast, the weight of the 
yeast, after fermentation, is not less but more than at 
first. This increase is from 5 to 12 per cent, by 
weight. The cause of it has been discussed by Pas¬ 
teur, but I believe definite evidence can now be fur¬ 
nished that it is due to the remarkable circumstance, 
that the nitrogenous material extracted from the 
yeast during fermentation may itself serve as food 
for the production of new yeast-cells. In that case, 
it is easily intelligible that the yeast should increase 
in weight. At the commencement of the fermenta¬ 
tion, and for some time afterwards, nitrogenous ma¬ 
terial is extracted from the cell-contents of the yeast 
by the liquid still rich in sugar. The residual living 
yeast behaves to this liquid like fresh yeast that has 
been added to beerwort,—it sprouts and forms new 
-cells which consume the dissolved nitrogenous ma¬ 
terial in reproducing the originally active cell-con¬ 
tents. Then, inasmuch as these new cells act upon 
sugar, there is again a separation of nitrogenous ma¬ 
terial, and this may continue to go on for months. 
The formation of new cell-membrane goes on pa¬ 
rallel with the production of new cells, and, since 
that consists of cellulose, the weight of the yeast is 
thus increased, while, at the same time, its relative 
amount of nitrogen decreases. The process just de¬ 
scribed may be made apparent if a litre of 10 per 
cent, sugar solution be completely fermented with 
15 c.c. moist yeast paste. If the clear liquid above 
the remaining yeast be filtered two or three times 
through a double filter, there will not be any trace 
of organized substance recognizable in the liquid. 
By boiling tliis for some time to remove alcohol, 
there remains 450 or 500 c.c., containing the nitro¬ 
genous substance that has been separated from the 
yeast in the fermentation. If some 30 or 40 grm. of 
sugar be dissolved in the liquid, and, after cooling to 
20° C., a trace of yeast* added to it, the whole being 
left in a small closed flask, fitted with a discharge- 
tube for gas dipping into water, it will be found that, 
after ten hours, there is distinct evolution of gas and 
a sensible deposit of yeast. The discharge of gas 
constantly augments, and after three or four days the 
yeast produced will amount to 450 to 600 milligrams 
in the pasty condition. After eight or ten days, 
the whole of the sugar will have disappeared. By 
repeating the same series of operations with tliis liquid 
the process is again repeated, and in this way I have 
succeeded in producing yeast of perfect activity four 
times successively in the same liquid. This yeast 
behaved towards sugar solution yeast in the same 
way as fresh yeast. 
The only precaution necessary for succeeding in 
this experiment is that, after the end of each fermen¬ 
tation, the filtered and evaporated liquid must be 
exactly neutralized with carbonate of potash, to pre¬ 
vent its becoming too acid. 
The slow progress of the fermentation when there 
is only a small quantity of yeast, or what is known 
as the after fermentation, is due to the circumstance 
that, while the nitrogenous and sulphuretted mate¬ 
rial transferred from the yeast-cell to the liquid in 
consequence of the metamorphosis taking place there, 
has not in itself the power of converting sugar into 
alcohol and carbonic acid. It nevertheless acquires 
that power again ; tliis happening by its serving as 
material for the production of new yeast-cells, and 
assuming in the cells that state of combination in 
which it produces decomposition of sugar. 
During fermentation a separation of the nitroge¬ 
nous cell-contents takes place ; one part remaining in 
the exhausted cell in an insoluble state, and that is 
the reason why the action of the yeast is limited. 
If all the nitrogenous constituents were separated 
from the cell, and they had the capability of serving 
again for the production of new cells, the process of 
fermentation would be a true perpetual motion. 
The cases of fermentation of sugar solution with 
washed beer-yeast, described above, constitute a 
tolerably good representation of all similar lands 
of fermentation. With a certain proportion of 
yeast, the fermentation is rapid, and the yeast de¬ 
creases in weight; with a very small amount of 
yeast, the fermentation is slow, and may last for 
months or years, as in the after fermentation or ma¬ 
turing of wine, and in this case there is an increase 
in the quantity of yeast. 
It is conceivable that in both cases the process is 
the same, and that the difference is due merely to the 
quantity of yeast; but if the continued formation of 
cells were a necessary condition of rapid fermenta¬ 
tion, then the number of cell vessels and the weight 
of cellulose should increase in the same ratio, as in 
the slow fermentation, while the fact is that the 
yeast decreases in weight in rapid fermentation. 
Disregarding mere opinions our actual knowledge 
of yeast and of its action is limited to the follow¬ 
ing :— 
1. Yeast consists of plant-cells, that develope and 
multiply in a liquid containing sugar and an albumi¬ 
nate, or some substance derived from an albuminate. 
The chief mass of the cell contents consists of a 
* For this purpose a piece of pasty yeast, the size of a pin’s 
head, is mixed with 10 c.c. water, and of this 1 c.c. is taken. 
