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We may still further increase this ratio by making our estimation
as soon as possible after the impregnation, or the addition of
the ferment. It will be readily understood why yeast, which is
composed of cells that bud and subsequently detach themselves
from one another, soon forms a deposit at the bottom of the
vessels. In consequence of this habit of growth, the cells
constantly covering each other prevents the lower layers from
having access to the oxygen held in solution in the liquid, which
is absorbed by the upper ones. Hence, these which are covered and
deprived of this gas act on the sugar without deriving any vital
benefit from the oxygen--a circumstance which must tend to
diminish the ratio of which we are speaking. Once more repeating
the preceding experiment, but stopping it as soon as we think
that the weight of yeast formed may be determined by the balance
(we find that this may be done twenty-four hours after
impregnation with an inappreciable quantity of yeast), in this
case the ratio between the weights of yeast and sugar is gr/024
yeast/0 gr. 09 sugar=1/4. This is the highest ratio we have been
able to obtain.

Under these conditions the fermentation of sugar is extremely
languid: the ratio obtained is very nearly the same that ordinary
fungoid growths would give. The carbonic acid evolved is
principally formed by the decompositions which result from the
assimilation of atmospheric oxygen. The yeast, therefore, lives
and performs its functions after the manner of ordinary fungi: so
far it is no longer a ferment, so to say; moreover, we might
expect to find it to cease to be a ferment at all if we could
only surround each cell separately with all the air that it
required. This is what the preceding phenomena teach us; we shall
have occasion to compare them later on with others which relate
to the vital action exercised on yeast by the sugar of milk.

We may here be permitted to make a digression.

In his work on fermentations, which M. Schutzenberger has
recently published, the author criticises the deductions that we
have drawn from the preceding experiments, and combats the
explanation which we have given of the phenomena of fermentation.
[Footnote: International Science Series, vol. xx, pp. 179-182.
London, 1876.--D. C. R.] It is an easy matter to show the weak
point of M. Schutzenberger's reasoning. We determined the power
of the ferment by the relation of the weight of sugar decomposed
to the weight of the yeast produced. M. Schutzenberger asserts
that in doing this we lay down a doubtful hypothesis, and he
thinks that this power, which he terms FERMENTATIVE ENERGY, may
be estimated more correctly by the quantity of sugar decomposed
by the unit-weight of yeast in unit-time; moreover, since our
experiments show that yeast is very vigorous when it has a
sufficient supply of oxygen, and that, in such a case, it can
decompose much sugar in a little time, M. Schutzenberger
concludes that it must then have great power as a ferment, even
greater than when it performs its functions without the aid of
air, since under this condition it decomposes sugar very slowly.
In short, he is disposed to draw from our observations the very
opposite conclusion to that which we arrived at.

M, Schutzenberger has failed to notice that the power of a
ferment is independent of the time during which it performs its
functions. We placed a trace of yeast in one litre of saccharine
wort; it propagated, and all the sugar was decomposed. Now,
whether the chemical action involved in this decomposition of
sugar had required for its completion one day, or one month, or
one year, such a factor was of no more importance in this matter
than the mechanical labour required to raise a ton of materials
from the ground to the top of a house would be affected by the
fact that it had taken twelve hours instead of one. The notion of
time has nothing to do with the definition of work. M.
Schutzenberger has not perceived that in introducing the
consideration of time into the definition of the power of a
ferment, he must introduce at the same time, that of the vital
activity of the cells which is independent of their character as
a ferment. Apart from the consideration of the relation existing
between the weight of fermentable substance decomposed and that
of ferment produced, there is no occasion to speak of
fermentations or of ferments. The phenomena of fermentation and
of ferments have been placed apart from others, precisely
because, in certain chemical actions, that ratio has been out of
proportion; but the time that these phenomena require for their
accomplishment has nothing to do with either their existence
proper, or with their power. The cells of a ferment may, under
some circumstances, require eight days for revival and
propagation, whilst, under other conditions, only a few hours are
necessary; so that, if we introduce the notion of time into our
estimate of their power of decomposition, we may be led to
conclude that in the first case that power was entirely wanting,
and that in the second case it was considerable, although all the
time we are dealing with the same organism--the identical
ferment.

M. Schutzenberger is astonished that fermentation can take place
in the presence of free oxygen, if, as we suppose, the
decomposition of the sugar is the consequence of the nutrition of
the yeast, at the expense of the combined oxygen, which yields
itself to the ferment. At all events, he argues, fermentation
ought to be slower in the presence of free oxygen. But why should
it be slower? We have proved that in the presence of oxygen the
vital activity of the cells increases, so that, as far as
rapidity of action is concerned, its power cannot be diminished.
It might, nevertheless, be weakened as a ferment, and this is
precisely what happens. Free oxygen imparts to the yeast a vital
activity, but at the same time impairs its power as yeast--qua
yeast, inasmuch as under this condition it approaches the state
in which it can carry on its vital processes after the manner of
an ordinary fungus; the mode of life, that is, in which the ratio
between the weight of sugar decomposed and the weight of the new
cells produced will be the same as holds generally among
organisms which are not ferments. In short, varying our form of
expression a little, we may conclude with perfect truth, from the
sum total of observed facts, that the yeast which lives in the
presence of oxygen and can assimilate as much of that gas as is
necessary to its perfect nutrition, ceases absolutely to be a
ferment at all. Nevertheless, yeast formed under these conditions
and subsequently brought into the presence of sugar, OUT OF THE
INFLUENCE OF AIR, would decompose more IN A GIVEN TIME than in
any other of its states. The reason is that yeast which has
formed in contact with air, having the maximum of free oxygen
that it can assimilate is fresher and possessed of greater vital
activity than that which has been formed without air or with an
insufficiency of air. M. Schutzenberger would associate this
activity with the notion of time in estimating the power of the
ferment; but he forgets to notice that yeast can only manifest
this maximum of energy under a radical change of its life
conditions; by having no more air at its disposal and breathing
no more free oxygen. In other words, when its respiratory power
becomes null, its fermentative power is at its greatest. M.
Schutzenberger asserts exactly the opposite (p. 151 of his work--
Paris, 1875) [Footnote: Page 182, English edition], and so
gratuitously places himself in opposition to facts.

In presence of abundant air supply, yeast vegetates with
extraordinary activity. We see this in the weight of new yeast,
comparatively large, that may be formed in the course of a few
hours. The microscope still more clearly shows this activity in
the rapidity of budding, and the fresh and active appearance of
all the cells. Fig. 6 represents the yeast of our last experiment
at the moment when we stopped the fermentation. Nothing has been
taken from imagination, all the groups have been faithfully
sketched as they were. [Footnote: This figure is on a scale of
300 diameters, most of the figures in this work being of 400
diameters].

[Illustration with caption: Fig. 6]

In passing it is of interest to note how promptly the preceding
results were turned to good account practically. In well-managed
distilleries, the custom of aerating the wort and the juices to
render them more adapted to fermentation, has been introduced.
The molasses mixed with water, is permitted to run in thin
threads through the air at the moment when the yeast is added.
Manufactories have been erected in which the manufacture of yeast
is almost exclusively carried on. The saccharine worts, after the
addition of yeast, are left to themselves, in contact with air,
in shallow vats of large superficial area, realizing thus on an
immense scale the conditions of the experiments which we
undertook in 1861, and which we have already described in
determining the rapid and easy multiplication of yeast in contact
with air.

The next experiment was to determine the volume of oxygen
absorbed by a known quantity of yeast, the yeast living in
contact with air, and under such conditions that the absorption
of air was comparatively easy and abundant.

[Illustration with caption: Fig. 7]

With this object we repeated the experiment that we performed
with the large-bottomed flask (Fig. 4), employing a vessel shaped
like Fig. B (Fig. 7), which is, in point of fact, the flask A
with its neck drawn out and closed in a flame, after the
introduction of a thin layer of some saccharine juice impregnated
with a trace of pure yeast. The following are the data and
results of an experiment of this kind.

We employed 60 cc. (about 2 fluid ounces) of yeast-water,
sweetened with two percent. of sugar and impregnated with a trace
of yeast. After having subjected our vessel to a temperature of
25 degrees C. (77 degrees F.) in an oven for fifteen hours, the
drawn-out point was brought under an inverted jar filled with
mercury and the point broken off. A portion of the gas escaped
and was collected in the jar. For 25 cc. of this gas we found,
after absorption by potash 20.6, and after absorption by
pyrogallic acid, 17.3. Taking into account the volume which
remained free in the flask, which held 315 cc., there was a total
absorption of 14.5 cc. (0.83 cub. in.) of oxygen. [Footnote: It
may be useful for the non-scientific reader to put it thus: that
the 25 cc. which escaped, being a fair sample of the whole gas in
the flask, and containing (1) 25-20.6=4.4 cc., absorbed by potash
and therefore due to carbonic acid, and (2) 20.6-17.3=3.3 cc.,
absorbed by pyrogallate, and therefore due to oxygen, and the
remaining 17.3 cc. being nitrogen, the whole gas in the flask,
which has a capacity of 312 cc., will contain oxygen in the above
portion and therefore its amount may be determined provided we
know the total gas in the flask before opening. On the other hand
we know that air normally contains approximately, 1-5 its volume
of oxygen, the rest being nitrogen, so that, by ascertaining the
diminution of the proportion in the flask, we can find how many
cubic centimeters have been absorbed by the yeast. The author,
however, has not given all the data necessary for accurate
calculation.--D.C.R.] The weight of the yeast, in a state of
dryness, was 0.035 gramme.

It follows that in the production of 35 milligrammes (0.524
grain) of yeast there was an absorption of 14 or 15 cc. (about
7/8 cub. in.) of oxygen, even supposing that the yeast was formed
entirely under the influence of that gas: this is equivalent to
not less than 414 cc. for 1 gramme of yeast (or about 33 cubic
inches for every 20 grains). [Footnote: This number is probably
too small; it is scarcely possible that the increase of weight in
the yeast, even under the exceptional conditions of the
experiment described, was not to some extent at least due to
oxidation apart from free oxygen, inasmuch as some of the cells
were covered by others. The increased weight of the yeast is
always due to the action of two distant modes of vital energy--
activity, namely, in presence and activity in absence of air. We
might endeavor to shorten the duration of the experiment still
further, in which case we would still more assimilate the life of
the yeast to that of ordinary moulds.]

Such is the large volume of oxygen necessary for the development
of one gramme of yeast when the plant can assimilate this gas
after the manner of an ordinary fungus.

Let us now return to the first experiment described in the
paragraph on page 292 in which a flask of three litres capacity
was filled with fermentable liquid, which, when caused to
ferment, yielded 2.25 grammes of yeast, under circumstances where
it could not obtain a greater supply of free oxygen than 16.5 cc.
(about one cubic inch). According to what we have just stated, if
this 2.25 grammes (34 grains) of yeast had not been able to live
without oxygen, in other words, if the original cells had been
unable to multiply otherwise than by absorbing free oxygen, the
amount of that gas required could not have been less than 2.25 X
4l4 cc., that is, 931.5 cc. (56.85 cubic inches). The greater
part of the 2.25 grammes, therefore, had evidently been produced
as the growth of an anaerobian plant.

Ordinary fungi likewise require large quantities of oxygen for
their development, as we may readily prove by cultivating any
mould in a closed vessel full of air, and then taking the weight
of plant formed and measuring the volume of oxygen absorbed. To
do this, we take a flask of the shape shown in Fig. 8, capable of
holding about 300 cc. (10 1/2 fluid ounces), and containing a
liquid adapted to the life of moulds. We boil this liquid, and
seal the drawn-out point after the steam has expelled the air
wholly or in part; we then open the flask in a garden or in a
room. Should a fungus-spore enter the flask, as will invariably
be the case in a certain number of flasks out of several used in
the experiment, except under special circumstances, it will
develop there and gradually absorb all the oxygen contained in
the air of the flask. Measuring the volume of this air, and
weighing, after drying, the amount of plant formed, we find that
for a certain quantity of oxygen absorbed we have a certain
weight of mycelium, or of mycelium together with its organs of
fructification. In an experiment of this kind, in which the plant
was weighed a year after its development, we found for 0.008
gramme (0.123 gram) of MYCELIUM, dried at 100 degrees C. (212
degrees F.), an absorption that amounted to not less than 43 cc.
(2.5 cubic inches) of oxygen at 25 degrees. These numbers,
however, must vary sensibly with the nature of the mould
employed, and also with the greater or less activity of its
development, because the phenomena is complicated by the presence
of accessory oxidations, such as we find in the case of mycoderma
vini and aceti, to which cause the large absorption of oxygen in
our last experiment may doubtless be attributed. [Footnote: In
these experiments, in which the moulds remain for a long time in
contact with a saccharine wort out of contact with oxygen--the
oxygen being promptly absorbed by the vital action of the plant
(see our Memoire sur les Generations dites Spontanees, p. 54.
note)--there is no doubt that an appreciable quantity of alcohol
is formed because the plant does not immediately lose vital
activity after the absorption of oxygen.

A 300 cc. (10-oz.) flask, containing 100 cc. of must, after the
air in it had been expelled by boiling, was open and immediately
re-closed on August 15th, 1873. A fungoid growth--a unique one,
of greenish-grey colour--developed from spontaneous impregnation,
and decolourized the liquid, which originally was of a yellowish-
brown. Some large crystals, sparkling like diamonds, of neutral
tartrate of lime, were precipitated, about a year afterwards,
long after the death of the plant, we examined this liquid. It
contained 0.3 gramme (4.6 grains) of alcohol, and 0.053 gramme
(0.8 grain) of vegetable matter, dried at 100 degrees C. (212
degrees F.). We ascertained that the spores of the fungus were
dead at the moment when the flask was opened. When sown, they did
not develop in the least degree.]

The conclusions to be drawn from the whole of the preceding facts
can scarcely admit of doubt. As for ourselves, we have no
hesitation in finding them the foundation of the true theory of
fermentation. In the experiments which we have described,
fermentation by yeast, that is to say, by the type of ferments
properly so called, is presented to us, in a word, as the direct
consequence of the processes of nutrition, assimilation and life,
when these are carried on without the agency of free oxygen. The
heat required in the accomplishment of that work must necessarily
have been borrowed from the decomposition of the fermentable
matter, that is from the saccharine substance which, like other
unstable substances, liberates heat in undergoing decomposition.
Fermentation by means of yeast appears, therefore, to be
essentially connected with the property possessed by this minute
cellular plant of performing its respiratory functions, somehow
or other, with oxygen existing combined in sugar. Its
fermentative power--which power must not be confounded with the
fermentative activity or the intensity of decomposition in a
given time--varies considerably between two limits, fixed by the
greatest and least possible access to free oxygen which the plant
has in the process of nutrition. If we supply it with a
sufficient quantity of free oxygen for the necessities of its
life, nutrition, and respiratory combustions, in other words, if
we cause it to live after the manner of a mould, properly so
called, it ceases to be a ferment, that is, the ratio between the
weight of the plant developed and that of the sugar decomposed,
which forms its principal food, is similar in amount to that in
the case of fungi. [Footnote: We find in M. Raulin's note that
"the minimum ratio between the weight of sugar and the weight of
organized matter, that is, the weight of fungoid growth which it
helps to form, may be expressed as 10/3.2=3.1." JULES RAULIN,
Etudes chimiques sur la vegetation. Recherches sur le
developpement d'une mucedinee dans un milieu artificiel, p. 192,
Paris, 1870. We have seen in the case of yeast that this ratio
may be as low as [Proofers note: unreadable symbol]] On the other
hand, if we deprive the yeast of air entirely, or cause it to
develop in a saccharine medium deprived of free oxygen, it will
multiply just as if air were present, although with less
activity, and under these circumstances its fermentative
character will be most marked; under these circumstances,
moreover, we shall find the greatest disproportion, all other
conditions being the same, between the weight of yeast formed and
the weight of sugar decomposed. Lastly, if free oxygen occurs in
varying quantities, the ferment-power of the yeast may pass
through all the degrees comprehended between the two extreme
limits of which we have just spoken. It seems to us that we could
not have a better proof of the direct relation that fermentation
bears to life, carried on in the absence of free oxygen, or with
a quantity of that gas insufficient for all the acts of nutrition
and assimilation.

Another equally striking proof of the truth of this theory is the
fact previously demonstrated that the ordinary moulds assume the
character of a ferment when compelled to live without air, or
with quantities of air too scant to permit of their organs having
around them as much of that element as is necessary for their
life as aerobian plants. Ferments, therefore, only possess in a
higher degree a character which belongs to many common moulds, if
not to all, and which they share, probably, more or less, with
all living cells, namely the power of living either an aerobian
or anaerobian life, according to the conditions under which they
are placed.

It may be readily understood how, in their state of aerobian
life, the alcoholic ferments have failed to attract attention.
These ferments are only cultivated out of contract with air, at
the bottom of liquids which soon become saturated with carbonic
acid gas. Air is only present in the earlier developments of
their germs, and without attracting the attention of the
operator, whilst in their state of anaerobian growth their life
and action are of prolonged duration. We must have recourse to
special experimental apparatus to enable us to demonstrate the
mode of life of alcoholic ferments under the influence of free
oxygen; it is their state of existence apart from air, in the
depths of liquids, that attracts all our attention. The results
of their action are, however, marvellous, if we regard the
products resulting from them, in the important industries of
which they are the life and soul. In the case of ordinary moulds,
the opposite holds good. What we want to use special experimental
apparatus for with them, is to enable us to demonstrate the
possibility of their continuing to live for a time out of contact
with air, and all our attention, in their case, is attracted by
the facility with which they develop under the influence of
oxygen. Thus the decomposition of saccharine liquids, which is
the consequence of the life of fungi without air, is scarcely
perceptible, and so is of no practical importance. Their aerial
life, on the other hand, in which they respire and accomplish
their process of oxidation under the influence of free oxygen is
a normal phenomenon, and one of prolonged duration which cannot
fail to strike the least thoughtful of observers. We are
convinced that a day will come when moulds will be utilised in
certain industrial operations, on account of their power in
destroying organic matter. The conversion of alcohol into vinegar
in the process of acetification and the production of gallic acid
by the action of fungi on wet gall nuts, are already connected
with this kind of phenomena. [Footnote: We shall show, some day,
that the processes of oxidation due to growth of fungi cause, in
certain decompositions, liberation of ammonia to a considerable
extent, and that by regulating their action we might cause them
to extract the nitrogen from a host of organic debris, as also,
by checking the production of such organisms, we might
considerably increase the proportion of nitrates in the
artificial nitrogenous substances. By cultivating the various
moulds on the surface of damp bread in a current of air we have
obtained an abundance of ammonia, derived from the decomposition
of the albuminoids effected by the fungoid life. The
decomposition of asparagus and several other animal or vegetable
substances has similar results.] On this last subject, the
important work of M. Van Tieghem (Annales Scientifiques de
l'Ecole Normale, Vol. vi.) may be consulted.

The possibility of living without oxygen, in the case of ordinary
moulds, is connected with certain morphological modifications
which are more marked in proportion as this faculty is itself
more developed. These changes in the vegetative forms are
scarcely perceptible, in the case of penicillium and mycoderma
vini, but they are very evident in the case of aspergillus,
consisting of a marked tendency on the part of the submerged
mycelial filaments to increase in diameter, and to develop cross
partitions at short intervals, so that they sometimes bear a
resemblance to chains of conidia. In mucor, again, they are very
marked, the inflated filaments which, closely interwoven, present
chains of cells, which fall off and bud, gradually producing a
mass of cells. If we consider the matter carefully, we shall see
that yeast presents the same characteristics. * * * *

It is a great presumption in favor of the truth of theoretical
ideas when the results of experiments undertaken on the strength
of those ideas are confirmed by various facts more recently added
to science, and when those ideas force themselves more and more
on our minds, in spite of a prima facie improbability. This is
exactly the character of those ideas which we have just
expounded. We pronounced them in 1861, and not only have they
remained unshaken since, but they have served to foreshadow new
facts, so that it is much easier to defend them in the present
day than it was to do so fifteen years ago. We first called
attention to them in various notes, which we read before the
Chemical Society of Paris, notably at its meetings of April 12th
and June 28th, 1861, and in papers in the Comtes rendus de
l'Academie des Sciences. It may be of some interest to quote
here, in its entirety, our communication of June 28th, 1861,
entitled, "Influences of Oxygen on the Development of Yeast and
on Alcoholic Fermentation," which we extract from the Bulletin de
la Societe Chimique de Paris:--