Constant - "Private Life of Napoleon Bonaparte, V5"

James H. McClintock - "Mormon Settlement in Arizona"

Ernest Scott - "Laperouse"

Mark Overton - "Jack Winters' Gridiron Chums"

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PHILADELPHIA, Pa. -- The Philadelphia literary world will celebrate the launch of two new players today, April 10th: Kay Square Press, a new publishing company focused on Philadelphia-area artists, their stories, and their art; and Kay Square's first release, 'With the Rich and Mighty: Emlen Etting of Philadelphia' (ISBN: 978-0-9815129-0-7), a critical biography by Kenneth C. Kaleta.

FlatSigned Press Alleges Don Imus Remarks Damage Legacy of President Gerald R. Ford
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Books: The Harvard Classics Volume 38

V >> Various >> The Harvard Classics Volume 38




Another equally exceptional characteristic of yeast and
fermentation in general consists in the small proportion which
the yeast that forms bears to the sugar that decomposes. In all
other known beings the weight of nutritive matter assimilated
corresponds with the weight of food used up, any difference that
may exist being comparatively small. The life of yeast is
entirely different. For a certain weight of yeast formed, we may
have ten times, twenty times, a hundred times as much sugar, or
even more decomposed, as we shall experimentally prove by-and-
bye; that is to say, that whilst the proportion varies in a
precise manner, according to conditions which we shall have
occasion to specify, it is also greatly out of proportion to the
weight of the yeast. We repeat, the life of no other being, under
its normal physiological conditions, can show anything similar.
The alcoholic ferments, therefore, present themselves to us as
plants which possess at least two singular properties: they can
live without air, that is without oxygen, and they can cause
decomposition to an amount which, though variable, yet, as
estimated by weight of product formed, is out of all proportion
to the weight of their own substance. These are facts of so great
importance, and so intimately connected with the theory of
fermentation, that it is indispensable to endeavour to establish
them experimentally, with all the exactness of which they will
admit.

The question before us is whether yeast is in reality an
anaerobian [Footnote: Capable of living without free oxygen--a
term invented by Pasteur.--En.] plant, and what quantities of
sugar it may cause to ferment, under the various conditions under
which we cause it to act.

The following experiments were undertaken to solve this double
problem:--We took a double-necked flask, of three litres (five
pints) capacity, one of the tubes being curved and forming an
escape for the gas; the other one, on the right hand side (Fig.
1), being furnished with a glass tap. We filled this flask with
pure yeast water, sweetened with 5 per cent, of sugar candy, the
flask being so full that there was not the least trace of air
remaining above the tap or in the escape tube; this artificial
wort had, however, been itself aerated. The curved tube was
plunged in a porcelain vessel full of mercury, resting on a firm
support. In the small cylindrical funnel above the tap, the
capacity of which was from 10 cc. to 15 cc. (about half a fluid
ounce) we caused to ferment, at a temperature of 20 degrees or 25
degrees C. (about 75 degrees F.), five or six cubic centimetres
of the saccharine liquid, by means of a trace of yeast, which
multiplied rapidly, causing fermentation, and forming a slight
deposit of yeast at the bottom of the funnel above the tap. We
then opened the tap, and some of the liquid in the funnel entered
the flask, carrying with it the small deposit of yeast, which was
sufficient to impregnate the saccharine liquid contained in the
flask. In this manner it is possible to introduce as small a
quantity of yeast as we wish, a quantity the weight of which, we
may say, is hardly appreciable. The yeast sown multiplies rapidly
and produces fermentation, the carbonic gas from which is
expelled into the mercury. In less than twelve days all the sugar
had disappeared, and the fermentation had finished. There was a
sensible deposit of yeast adhering to the sides of the flask;
collected and dried it weighed 2.25 grammes (34 grains). It is
evident that in this experiment the total amount of yeast formed,
if it required oxygen to enable it to live, could not have
absorbed, at most, more than the volume which was originally held
in solution in the saccharine liquid, when that was exposed to
the air before being introduced into the flask.

[Illustration with caption: Fig. 1]

Some exact experiments conducted by M. Raulin in our laboratory
have established the fact that saccharine worts, like water, soon
become saturated when shaken briskly with an excess of air, and
also that they always take into solution a little less air than
saturated pure water contains under the same conditions of
temperature and pressure. At a temperature of 25 degrees C. (77
degrees F.), therefore, if we adopt the coefficient of the
solubility of oxygen in water given in Bunsen's tables, we find
that 1 litre (1 3/4 pints) of water saturated with air contains
5.5 cc. (0.3 cubic inch) of oxygen. The three litres of yeast-
water in the flask, supposing it to have been saturated, contains
less than 16.5 cc. (1 cubic inch) of oxygen, or, in weight, less
than 23 milligrammes (0.35 grains). This was the maximum amount
of oxygen, supposing the greatest possible quantity to have been
absorbed, that was required by the yeast formed in the
fermentation of 150 grammes (4.8 Troy ounces) of sugar. We shall
better understand the significance of this result later on. Let
us repeat the foregoing experiment, but under altered conditions.
Let us fill, as before, our flask with sweetened yeast-water, but
let this first be boiled, so as to expel all the air it contains.
To effect this we arrange our apparatus as represented in the
accompanying sketch. (Fig 2.) We place our flask, A, on a tripod
above a gas flame, and in place of the vessel of mercury
substitute a porcelain dish, under which we can put a gas flame,
and Which contains some fermentable, saccharine liquid, similar
to that with which the flask is filled. We boil the liquid in the
flask and that in the basin simultaneously, and then let them
cool down together, so that as the liquid in the flask cools some
of the liquid is sucked from the basin into the flask. From a
trial experiment which we conducted, determining the quantity of
oxygen that remained in solution in the liquid after cooling,
according to M. Schutzenberger's valuable method, by means of
hydrosulphite of soda [Footnote: NaHSO2, now called sodium
hyposulphite.--D.C.R.], we found that the three litres in the
flask, treated as we have described, contained less than one
milligramme (0.015 grain) of oxygen. At the same time we
conducted another experiment, by way of comparison (Fig. 3). We
took a flask, B, of larger capacity than the former one, which we
filled about half with the same volume as before of a saccharine
liquid of identically the same composition. This liquid had been
previously freed from alterative germs by boiling. In the funnel
surmounting A, we put a few cubic centimetres of saccharine
liquid in a state of fermentation, and when this small quantity
of liquid was in full fermentation, and the yeast in it was young
and vigorous, we opened the tap, closing it again immediately, so
that a little of the liquid and yeast still remained in the
funnel. By this means we caused the liquid in A to ferment. We
also impregnated the liquid in B with some yeast taken from the
funnel of A. We then replaced the porcelain dish in which the
curved escape tube of A had been plunged, by a vessel filled with
mercury. The following is a description of two of these
comparative fermentations and the results they gave.

[Illustration with caption: Fig 2]

[Illustration with caption: Fig. 3]

The fermentable liquid was composed of yeast-water sweetened with
5 per cent, of sugar--candy; the ferment employed was
sacchormyces pastorianus.

The impregnation took place on January 20th. The flasks were
placed in an oven at 25 degrees (77 degrees F.).

FLASK A, WITHOUT AIR.

January 21st.--Fermentation commenced; a little frothy liquid
issued from the escape tube and covered the mercury.

The following days, fermentation was active. Examining the yeast
mixed with the froth that was expelled into the mercury by the
evolution of carbonic acid gas, we find that it was very fine,
young, and actively budding.

February 3rd.--Fermentation still continued, showing itself by a
number of little bubbles rising from the bottom of the liquid,
which had settled bright. The yeast was at the bottom in the form
of a deposit.

February 7th.--Fermentation still continued, but very languidly.

February 9th.--A very languid fermentation still went on,
discernible in little bubbles rising from the bottom of the
flask.

FLASK B, WITH AIR.

January 21st.--A sensible development of yeast.

The following days, fermentation was active, and there was an
abundant froth on the surface of the liquid.

February 1st.--All symptoms of fermentation had ceased.

As the fermentation in A would have continued a long time, being
so very languid, and as that in B had been finished for several
days, we brought to a close our two experiments on February 9th.
To do this we poured off the liquids in A and B, collecting the
yeasts on tared filters. Filtration was an easy matter, more
especially in the case of A. Examining the yeasts under the
microscope, immediately after decantation, we found that both of
them remained very pure. The yeast in A was in little clusters,
the globules of which were collected together, and appeared by
their well-defined borders to be ready for an easy revival in
contact with air.

As might have been expected, the liquid in flask B did not
contain the least trace of sugar; that in the flask A still
contained some, as was evident from the non-completion of
fermentation, but not more than 4.6 grammes (71 grains). Now, as
each flask originally contained three litres of liquid holding in
solution 5 per cent of sugar, it follows that 150 grammes (2,310
grains) of sugar had fermented in the flask B, and 145.4 grammes
(2,239.2 grains) in the flask A. The weights of yeast after
drying at 100 degrees C. (212 degrees F.) were--

For the flask B, with air. ... ..1,970 grammes (30.4 grains). For
the flask A, without air ... 1,368 grammes [Footnote: This appears
to be a misprint for 1.638 grammes=25.3 grains.--D. C. R.].

The proportions were 1 of yeast to 76 of fermented sugar in the
first case, and 1 of yeast to 89 of fermented sugar in the
second.

From these facts the following consequences may be deduced:

1. The fermentable liquid (flask B), which since it had been in
contact with air, necessarily held air in solution, although not
to the point of saturation, inasmuch as it had been once boiled
to free it from all foreign germs, furnished a weight of yeast
sensibly greater than that yielded by the liquid which contained
no air at all (flask A) or, at least, which could only have
contained an exceedingly minute quantity.

2. This same slightly aerated fermentable liquid fermented much
more rapidly than the other. In eight or ten days it contained no
more sugar; while the other, after twenty days, still contained
an appreciable quantity.

Is this last fact to be explained by the greater quantity of
yeast formed in B? By no means. At first, when the air has access
to the liquid, much yeast is formed and little sugar disappears,
as we shall prove immediately; nevertheless the yeast formed in
contact with the air is more active than the other. Fermentation
is correlative first to the development of the globules, and then
to the continued life of those globules once formed. The more
oxygen these last globules have at their disposal during their
formation, the more vigorous, transparent, and turgescent, and,
as a consequence of this last quality, the more active they are
in decomposing sugar. We shall hereafter revert to these facts.

3. In the airless flask the proportion of yeast to sugar was
1/59; it was only 1/79 in the flask which had air at first.

The proportion that the weight of yeast bears to the weight of
the sugar is, therefore, variable, and this variation depends, to
a certain extent, upon the presence of air and the possibility of
oxygen being absorbed by the yeast. We shall presently show that
yeast possesses the power of absorbing that gas and emitting
carbonic acid, like ordinary fungi, that even oxygen may be
reckoned amongst the number of food-stuffs that may be
assimilated by this plant, and that this fixation of oxygen in
yeast, as well as the oxidations resulting from it, have the most
marked effect on the life of yeast, on the multiplication of its
cells, and on their activity as ferments acting upon sugar,
whether immediately or afterwards, apart from supplies of oxygen
or air.

In the preceding experiment, conducted without the presence of
air, there is one circumstance particularly worthy of notice.
This experiment succeeds, that is to say, the yeast sown in the
medium deprived of oxygen develops, only when this yeast is in a
state of great vigour. We have already explained the meaning of
this last expression. But we wish now to call attention to a very
evident fact in connection with this point. We impregnate a
fermentable liquid; yeast develops and fermentation appears. This
lasts for several days and then ceases. Let us suppose that, from
the day when fermentation first appears in the production of a
minute froth, which gradually increases until it whitens the
surface of the liquid, we take, every twenty-four hours, or at
longer intervals, a trace of the yeast deposited on the bottom of
the vessel and use it for starting fresh fermentations.
Conducting these fermentations all under precisely the same
conditions of temperature, character and volume of liquid, let us
continue this for a prolonged time, even after the original
fermentation is finished. We shall have no difficulty in seeing
that the first signs of action in each of our series of second
fermentations appear always later and later in proportion to the
length of time that has elapsed from the commencement of the
original fermentation. In other words, the time necessary for the
development of the germs and the production of that amount of
yeast sufficient to cause the first appearance of fermentation
varies with the state of the impregnating cells, and is longer in
proportion as the cells are further removed from the period of
their formation. It is essential, in experiments of this kind,
that the quantities of yeast successively taken should be as
nearly as possible equal in weight or volume, since, celeris
paribus, fermentations manifest themselves more quickly the
larger the quantity of yeast employed in impregnation.

If we compare under the microscope the appearance and character
of the successive quantities of yeast taken, we shall see plainly
that the structure of the cells undergoes a progressive change.
The first sample which we take, quite at the beginning of the
original fermentation, generally gives us cells rather larger
than those later on, and possessing a remarkable tenderness.
Their walls are exceedingly thin, the consistency and softness of
their protoplasm is akin to fluidity, and their granular contents
appear in the form of scarcely visible spots. The borders of the
cells soon become more marked, a proof that their walls undergo a
thickening; their protoplasm also becomes denser, and the
granulations more distinct. Cells of the same organ, in the
states of infancy and old age, should not differ more than the
cells of which we are speaking, taken in their extreme states.
The progressive changes in the cells, after they have acquired
their normal form and volume, clearly demonstrate the existence
of a chemical work of a remarkable intensity, during which their
weight increases, although in volume they undergo no sensible
change, a fact that we have often characterized as "the continued
life of cells already formed." We may call this work a process of
maturation on the part of the cells, almost the same that we see
going on in the case of adult beings in general, which continue
to live for a long time, even after they have become incapable of
reproduction, and long after their volume has become permanently
fixed.

This being so, it is evident, we repeat, that, to multiply in a
fermentable medium, quite out of contact with oxygen, the cells
of yeast must be extremely young, full of life and health, and
still under the influence of the vital activity which they owe to
the free oxygen which has served to form them, and which they
have perhaps stored up for a time. When older, they reproduce
themselves with much difficulty when deprived of air, and
gradually become more languid; and if they do multiply, it is in
strange and monstrous forms. A little older still, they remain
absolutely inert in a medium deprived of free oxygen. This is not
because they are dead; for in general they may be revived in a
marvellous manner in the same liquid if it has been first aerated
before they are sown. It would not surprise us to learn that at
this point certain preconceived ideas suggest themselves to the
mind of an attentive reader on the subject of the causes that may
serve to account for such strange phenomena in the life of these
beings which our ignorance hides under the expressions of YOUTH
and AGE; this, however, is a subject which we cannot pause to
consider here.

At this point we must observe--for it is a matter of great
importance--that in the operations of the brewer there is always
a time when the yeasts are in this state of vigorous youth of
which we have been speaking, acquired under the influence of free
oxygen, since all the worts and the yeasts of commerce are
necessarily manipulated in contact with air, and so impregnated
more or less with oxygen. The yeast immediately seizes upon this
gas and acquires a state of freshness and activity, which permits
it to live afterwards out of contact with air, and to act as a
ferment. Thus, in ordinary brewery practice, we find the yeast
already formed in abundance even before the earliest external
signs of fermentation have made their appearance. In this first
phase of its existence, yeast lives chiefly like an ordinary
fungus.

From the same circumstances it is clear that the brewer's
fermentations may, speaking quite strictly, last for an
indefinite time, in consequence of the unceasing supply of fresh
wort, and from the fact, moreover, that the exterior air is
constantly being introduced during the work, and that the air
contained in the fresh worts keeps up the vital activity of the
yeast, as the act of breathing keeps up the vigour and life of
cells in all living beings. If the air could not renew itself in
any way, the vital activity which the cells originally received,
under its influence, would become more and more exhausted, and
the fermentation eventually come to an end.

We may recount one of the results obtained in other experiments
similar to the last, in which, however, we employed yeast which
was still older than that used for our experiment with flask A
(Fig. 2), and moreover took still greater precautions to prevent
the presence of air. Instead of leaving the flask, as well as the
dish, to cool slowly, after having expelled all air by boiling,
we permitted the liquid in the dish to continue boiling whilst
the flask was being cooled by artificial means; the end of the
escape tube was then taken out of the still boiling dish and
plunged into the mercury trough. In impregnating the liquid,
instead of employing the contents of the small cylindrical funnel
whilst still in a state of fermentation, we waited until this was
finished. Under these conditions, fermentation was still going on
in our flask, after a lapse of three months. We stopped it and
found that 0.255 gramme (3.9 grains) of yeast had been formed,
and that 45 grammes (693 grains) of sugar had fermented, the
ratio between the weights of yeast and sugar being thus 0.255
divided by 45 = 1 divided by 176. In this experiment the yeast
developed with much difficulty, by reason of the conditions to
which it had been subjected. In appearance the cells varied much,
some were to be found large, elongated, and of tubular aspect,
some seemed very old and were extremely granular, whilst others
were more transparent. All of them might be considered abnormal
cells.

In such experiments we encounter another difficulty. If the yeast
sown in the non-aerated fermentable liquid is in the least degree
impure, especially if we use sweetened yeast-water, we may be
sure that alcoholic fermentation will soon cease, if, indeed, it
ever commences, and that accessory fermentations will go on. The
vibrios of butyric fermentation, for instance, will propagate
with remarkable facility under these circumstances. Clearly then,
the purity of the yeast at the moment of impregnation, and the
purity of the liquid in the funnel, are conditions indispensable
to success.

To secure the latter of these conditions, we close the funnel, as
shown in FIG. 2, by means of a cork pierced with two holes,
through one of which a short tube passes, to which a short length
of india-rubber tubing provided with a glass stopper is attached;
through the other hole a thin curved tube is passed. Thus fitted,
the funnel can answer the same purposes as our double-necked
flasks. A few cubic centimetres of sweetened yeast-water are put
in it and boiled, so that the steam may destroy any germs
adhering to the sides; and when cold the liquid is impregnated by
means of a trace of pure yeast, introduced through the glass-
stoppered tube. If these precautions are neglected, it is
scarcely possible to secure a successful fermentation in our
flasks, because the yeast sown is immediately held in check by a
development of anaerobian vibrios. For greater security, we may
add to the fermentable liquid, at the moment when it is prepared,
a very small quantity of tartaric acid, which will prevent the
development of butyric vibrios.

[Illustration with caption: Fig. 4.]

The variation of the ratio between the weight of the yeast and
that of the sugar decomposed by it now claims special attention.
Side by side with the experiments which we have just described,
we conducted a third lot by means of the flask C (Fig. 4),
holding 4.7 litres (8 1/2 pints), and fitted up like the usual
two-necked flasks, with the object of freeing the fermentable
liquid from foreign germs, by boiling it to begin with, so that
we might carry on our work under conditions of purity. The volume
of yeast-water (containing 5 per cent. of sugar) was only 200 cc.
(7 fl. oz.), and consequently, taking into account the capacity
of the flask, It formed but a very thin layer at the bottom. On
the day after impregnation the deposit of yeast was already
considerable, and forty-eight hours afterwards the fermentation
was completed. On the third day we collected the yeast after
having analyzed the gas contained in the flask. This analysis was
easily accomplished by placing the flask in a hot-water bath,
whilst the end of the curved tube was plunged under a cylinder of
mercury. The gas contained 41.4 per cent. of carbonic acid, and,
after the absorption, the remaining air contained:--

Oxygen . ... . ... . ... . ... . ... . ... . ... ... 19.7

Nitrogen . ... . ... . ... . ... . ... . ... . ... . 80.3

100.0

Taking into consideration the volume of this flask, this shows a
minimum of 50 cc. (3.05 cub. in.) of oxygen to have been absorbed
by the yeast. The liquid contained no more sugar, and the weight
of the yeast, dried at a temperature of 100 degrees C (212
degrees F.), was 0.44 grammes. The ratio between the weights of
yeast and sugar is 0.44/10=1/22.7 [Footnote: 200 cc. of liquid
were used, which, as containing 3 per cent., had in solution 10
grammes of sugar.--D.C.R.]. On this occasion, where we had
increased the quantity of oxygen held in solution, so as to yield
itself for assimilation at the beginning and during the earlier
developments of the yeast, we found instead of the previous ratio
of 1/76 that of 1/23.

[Illustration with caption: Fig. 5]

The next experiment was to increase the proportion of oxygen to a
still greater extent, by rendering the diffusion of gas a more
easy matter than in a flask, the air in which is in a state of
perfect quiescence. Such a state of matters hinders the supply of
oxygen, inasmuch as the carbonic acid, as soon as it is
liberated, at once forms an immovable layer on the surface of the
liquid, and so separates off the oxygen. To effect the purpose of
our present experiment, we used flat basins having glass bottoms
and low sides, also of glass, in which the depth of the liquid is
not more than a few millimetres (less than 1/4 inch) (Fig. 5). The
following is one of our experiments so conducted:--On April 16th,
1860, we sowed a trace of beer yeast ("high" yeast) in 200 cc. (7
fl. oz.) of a saccharine liquid containing 1.720 grammes (26.2
grains) of sugar-candy. From April 18th our yeast was in good
condition and well developed. We collected it, after having added
to the liquid a few drops of concentrated sulphuric acid, with
the object of checking the fermentation to a great extent, and
facilitating filtration. The sugar remaining in the filtered
liquid, determined by Fehling's solution, showed that 1.04
grammes (16 grains) of sugar had disappeared. The weight of the
yeast, dried at 100 degrees C. (212 degrees F.), was 0.127 gramme
(2 grains), which gives us the ratio between the weight of the
yeast and that of the fermented sugar 0.123/1.04=1/8.1, which is
considerably higher than the preceding ones.