the chief known constituents of the crust of the earth may have formed
part of living bodies; that they may be the "ash" of protoplasm; that the
"_rupes saxei_" are not only _"temporis,"_ but "_vitae filiae_"; and,
consequently, that the time during which life has been active on the
globe may be indefinitely greater than the period, the commencement of
which is marked by the oldest known rocks, whether fossiliferous or
unfossiliferous.
And thus we are led to see where the solution of a great problem and
apparent paradox of geology may lie. Satisfactory evidence now exists
that some animals in the existing world have been derived by a process of
gradual modification from pre-existing forms. It is undeniable, for
example, that the evidence in favour of the derivation of the horse from
the later tertiary _Hipparion_, and that of the _Hipparion_ from
_Anchitherium_, is as complete and cogent as such evidence can reasonably
be expected to be; and the further investigations into the history of the
tertiary mammalia are pushed, the greater is the accumulation of evidence
having the same tendency. So far from palaeontology lending no support to
the doctrine of evolution--as one sees constantly asserted--that
doctrine, if it had no other support, would have been irresistibly forced
upon us by the palaeontological discoveries of the last twenty years.
If, however, the diverse forms of life which now exist have been produced
by the modification of previously-existing less divergent forms, the
recent and extinct species, taken as a whole, must fall into series which
must converge as we go back in time. Hence, if the period represented by
the rocks is greater than, or co-extensive with, that during which life
has existed, we ought, somewhere among the ancient formations, to arrive
at the point to which all these series converge, or from which, in other
words, they have diverged--the primitive undifferentiated protoplasmic
living things, whence the two great series of plants and animals have
taken their departure.
But, as a matter of fact, the amount of convergence of series, in
relation to the time occupied by the deposition of geological formations,
is extraordinarily small. Of all animals the higher _Vertebrata_ are the
most complex; and among these the carnivores and hoofed animals
(_Ungulata_) are highly differentiated. Nevertheless, although the
different lines of modification of the _Carnivora_ and those of the
_Ungulata_, respectively, approach one another, and, although each group
is represented by less differentiated forms in the older tertiary rocks
than at the present day, the oldest tertiary rocks do not bring us near
the primitive form of either. If, in the same way, the convergence of the
varied forms of reptiles is measured against the time during which their
remains are preserved--which is represented by the whole of the tertiary
and mesozoic formations--the amount of that convergence is far smaller
than that of the lines of mammals between the present time and the
beginning of the tertiary epoch. And it is a broad fact that, the lower
we go in the scale of organization, the fewer signs are there of
convergence towards the primitive form from whence all must have
diverged, if evolution be a fact. Nevertheless, that it is a fact in some
cases, is proved, and I, for one, have not the courage to suppose that
the mode in which some species have taken their origin is different from
that in which the rest have originated.
What, then, has become of all the marine animals which, on the hypothesis
of evolution, must have existed in myriads in those seas, wherein the
many thousand feet of Cambrian and Laurentian rocks now devoid, or almost
devoid, of any trace of life were deposited?
Sir Charles Lyell long ago suggested that the azoic character of these
ancient formations might be due to the fact that they had undergone
extensive metamorphosis; and readers of the "Principles of Geology" will
be familiar with the ingenious manner in which he contrasts the theory of
the Gnome, who is acquainted only with the interior of the earth, with
those of ordinary philosophers, who know only its exterior.
The metamorphism contemplated by the great modern champion of rational
geology is, mainly, that brought about by the exposure of rocks to
subterranean heat; and where no such heat could be shown to have
operated, his opponents assumed that no metamorphosis could have taken
place. But the formation of greensand, and still more that of the "red
clay" (if the _Challenger_ hypothesis be correct) affords an insight into
a new kind of metamorphosis--not igneous, but aqueous--by which the
primitive nature of a deposit may be masked as completely as it can be by
the agency of heat. And, as Wyville Thomson suggests, in the passage I
have quoted above (p. 17), it further enables us to assign a new cause
for the occurrence, so puzzling hitherto, of thousands of feet of
unfossiliferous fine-grained schists and slates, in the midst of
formations deposited in seas which certainly abounded in life. If the
great deposit of "red clay" now forming in the eastern valley of the
Atlantic were metamorphosed into slate and then upheaved, it would
constitute an "azoic" rock of enormous extent. And yet that rock is now
forming in the midst of a sea which swarms with living beings, the great
majority of which are provided with calcareous or silicious shells and
skeletons; and, therefore, are such as, up to this time, we should have
termed eminently preservable.
Thus the discoveries made by the _Challenger_ expedition, like all recent
advances in our knowledge of the phenomena of biology, or of the changes
now being effected in the structure of the surface of the earth, are in
accordance with and lend strong support to, that doctrine of
Uniformitarianism, which, fifty years ago, was held only by a small
minority of English geologists--Lyell, Scrope, and De la Beche--but now,
thanks to the long-continued labours of the first two, and mainly to
those of Sir Charles Lyell, has gradually passed from the position of a
heresy to that of catholic doctrine.
Applied within the limits of the time registered by the known fraction of
the crust of the earth, I believe that uniformitarianism is unassailable.
The evidence that, in the enormous lapse of time between the deposition
of the lowest Laurentian strata and the present day, the forces which
have modified the surface of the crust of the earth were different in
kind, or greater in the intensity of their action, than those which are
now occupied in the same work, has yet to be produced. Such evidence as
we possess all tends in the contrary direction, and is in favour of the
same slow and gradual changes occurring then as now.
But this conclusion in nowise conflicts with the deductions of the
physicist from his no less clear and certain data. It may be certain that
this globe has cooled down from a condition in which life could not have
existed; it may be certain that, in so cooling, its contracting crust
must have undergone sudden convulsions, which were to our earthquakes as
an earthquake is to the vibration caused by the periodical eruption of a
Geyser; but in that case, the earth must, like other respectable parents,
have sowed her wild oats, and got through her turbulent youth, before we,
her children, have any knowledge of her.
So far as the evidence afforded by the superficial crust of the earth
goes, the modern geologist can, _ex animo_, repeat the saying of Hutton,
"We find no vestige of a beginning--no prospect of an end." However, he
will add, with Hutton, "But in thus tracing back the natural operations
which have succeeded each other, and mark to us the course of time past,
we come to a period in which we cannot see any further." And if he seek
to peer into the darkness of this period, he will welcome the light
proffered by physics and mathematics.
IV
YEAST
[1871]
It has been known, from time immemorial, that the sweet liquids which may
be obtained by expressing the juices of the fruits and stems of various
plants, or by steeping malted barley in hot water, or by mixing honey
with water--are liable to undergo a series of very singular changes, if
freely exposed to the air and left to themselves, in warm weather.
However clear and pellucid the liquid may have been when first prepared,
however carefully it may have been freed, by straining and filtration,
from even the finest visible impurities, it will not remain clear. After
a time it will become cloudy and turbid; little bubbles will be seen
rising to the surface, and their abundance will increase until the liquid
hisses as if it were simmering on the fire. By degrees, some of the solid
particles which produce the turbidity of the liquid collect at its
surface into a scum, which is blown up by the emerging air-bubbles into a
thick, foamy froth. Another moiety sinks to the bottom, and accumulates
as a muddy sediment, or "lees."
When this action has continued, with more or less violence, for a certain
time, it gradually moderates. The evolution of bubbles slackens, and
finally comes to an end; scum and lees alike settle at the bottom, and
the fluid is once more clear and transparent. But it has acquired
properties of which no trace existed in the original liquid. Instead of
being a mere sweet fluid, mainly composed of sugar and water, the sugar
has more or less completely disappeared; and it has acquired that
peculiar smell and taste which we call "spirituous." Instead of being
devoid of any obvious effect upon the animal economy, it has become
possessed of a very wonderful influence on the nervous system; so that in
small doses it exhilarates, while in larger it stupefies, and may even
destroy life.
Moreover, if the original fluid is put into a still, and heated
moderately, the first and last product of its distillation is simple
water; while, when the altered fluid is subjected to the same process,
the matter which is first condensed in the receiver is found to be a
clear, volatile substance, which is lighter than water, has a pungent
taste and smell, possesses the intoxicating powers of the fluid in an
eminent degree, and takes fire the moment it is brought in contact with a
flame. The Alchemists called this volatile liquid, which they obtained
from wine, "spirits of wine," just as they called hydrochloric acid
"spirits of salt," and as we, to this day, call refined turpentine
"spirits of turpentine." As the "spiritus," or breath, of a man was
thought to be the most refined and subtle part of him, the intelligent
essence of man was also conceived as a sort of breath, or spirit; and, by
analogy, the most refined essence of anything was called its "spirit."
And thus it has come about that we use the same word for the soul of man
and for a glass of gin.
At the present day, however, we even more commonly use another name for
this peculiar liquid--namely, "alcohol," and its origin is not less
singular. The Dutch physician, Van Helmont, lived in the latter part of
the sixteenth and the beginning of the seventeenth century--in the
transition period between alchemy and chemistry--and was rather more
alchemist than chemist. Appended to his "Opera Omnia," published in 1707,
there is a very needful "Clavis ad obscuriorum sensum referendum," in
which the following passage occurs.--
"ALCOHOL.--Chymicis est liquor aut pulvis summé subtilisatus, vocabulo
Orientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_
speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat
... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorum
cancri summé subtilisatus _alcohol_ audit, haud aliter ac spiritus
rectificatissimi _alcolisati_ dicuntur."
Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, so
late as the middle of the last century, the English lexicographer, Nathan
Bailey, defines "alcohol" as "the pure substance of anything separated
from the more gross, a very fine and impalpable powder, or a very pure,
well-rectified spirit." But, by the time of the publication of
Lavoisier's "Traité Elémentaire de Chimie," in 1789, the term "alcohol,"
"alkohol," or "alkool" (for it is spelt in all three ways), which Van
Helmont had applied primarily to a fine powder, and only secondarily to
spirits of wine, had lost its primary meaning altogether; and, from the
end of the last century until now, it has, I believe, been used
exclusively as the denotation of spirits of wine, and bodies chemically
allied to that substance.
The process which gives rise to alcohol in a saccharine fluid is known
tones as "fermentation"; a term based upon the apparent boiling up or
"effervescence" of the fermenting liquid, and of Latin origin.
Our Teutonic cousins call the same process "gähren," "gäsen," "göschen,"
and "gischen"; but, oddly enough, we do not seem to have retained their
verb or their substantive denoting the action itself, though we do use
names identical with, or plainly derived from, theirs for the scum and
lees. These are called, in Low German, "gäscht" and "gischt"; in Anglo-
Saxon, "gest," "gist," and "yst," whence our "yeast." Again, in Low
German and in Anglo-Saxon there is another name for yeast, having the
form "barm," or "beorm"; and, in the Midland Counties, "barm" is the name
by which yeast is still best known. In High German, there is a third name
for yeast, "hefe," which is not represented in English, so far as I know.
All these words are said by philologers to be derived from roots
expressive of the intestine motion of a fermenting substance. Thus "hefe"
is derived from "heben," to raise; "barm" from "beren" or "bären," to
bear up; "yeast," "yst," and "gist," have all to do with seething and
foam, with "yeasty" waves, and "gusty" breezes.
The same reference to the swelling up of the fermenting substance is seen
in the Gallo-Latin terms "levure" and "leaven."
It is highly creditable to the ingenuity of our ancestors that the
peculiar property of fermented liquids, in virtue of which they "make
glad the heart of man," seems to have been known in the remotest periods
of which we have any record. All savages take to alcoholic fluids as if
they were to the manner born. Our Vedic forefathers intoxicated
themselves with the juice of the "soma"; Noah, by a not unnatural
reaction against a superfluity of water, appears to have taken the
earliest practicable opportunity of qualifying that which he was obliged
to drink; and the ghosts of the ancient Egyptians were solaced by
pictures of banquets in which the wine-cup passes round, graven on the
walls of their tombs. A knowledge of the process of fermentation,
therefore, was in all probability possessed by the prehistoric
populations of the globe; and it must have become a matter of great
interest even to primaeval wine-bibbers to study the methods by which
fermented liquids could be surely manufactured. No doubt it was soon
discovered that the most certain, as well as the most expeditious, way of
making a sweet juice ferment was to add to it a little of the scum, or
lees, of another fermenting juice. And it can hardly be questioned that
this singular excitation of fermentation in one fluid, by a sort of
infection, or inoculation, of a little ferment taken from some other
fluid, together with the strange swelling, foaming, and hissing of the
fermented substance, must have always attracted attention from the more
thoughtful. Nevertheless, the commencement of the scientific analysis of
the phenomena dates from a period not earlier than the first half of the
seventeenth century.
At this time, Van Helmont made a first step, by pointing out that the
peculiar hissing and bubbling of a fermented liquid is due, not to the
evolution of common air (which he, as the inventor of the term "gas,"
calls "gas ventosum"), but to that of a peculiar kind of air such as is
occasionally met with in caves, mines, and wells, and which he calls "gas
sylvestre."
But a century elapsed before the nature of this "gas sylvestre," or, as
it was afterwards called, "fixed air," was clearly determined, and it was
found to be identical with that deadly "choke-damp" by which the lives of
those who descend into old wells, or mines, or brewers' vats, are
sometimes suddenly ended; and with the poisonous aëriform fluid which is
produced by the combustion of charcoal, and now goes by the name of
carbonic acid gas.
During the same time it gradually became evident that the presence of
sugar was essential to the production of alcohol and the evolution of
carbonic acid gas, which are the two great and conspicuous products of
fermentation. And finally, in 1787, the Italian chemist, Fabroni, made
the capital discovery that the yeast ferment, the presence of which is
necessary to fermentation, is what he termed a "vegeto-animal" substance;
that is, a body which gives of ammoniacal salts when it is burned, and
is, in other ways, similar to the gluten of plants and the albumen and
casein of animals.
These discoveries prepared the way for the illustrious Frenchman,
Lavoisier, who first approached the problem of fermentation with a
complete conception of the nature of the work to be done. The words in
which he expresses this conception, in the treatise on elementary
chemistry to which reference has already been made, mark the year 1789 as
the commencement of a revolution of not less moment in the world of
science than that which simultaneously burst over the political world,
and soon engulfed Lavoisier himself in one of its mad eddies.
"We may lay it down as an incontestable axiom that, in all the operations
of art and nature, nothing is created; an equal quantity of matter exists
both before, and after the experiment: the quality and quantity of the
elements remain precisely the same, and nothing takes place beyond
changes and modifications in the combinations of these elements. Upon
this principle the whole art of performing chemical experiments depends;
we must always suppose an exact equality between the elements of the body
examined and those of the products of its analysis.
"Hence, since from must of grapes we procure alcohol and carbonic acid, I
have an undoubted right to suppose that must consists of carbonic acid
and alcohol. From these premisses we have two modes of ascertaining what
passes during vinous fermentation: either by determining the nature of,
and the elements which compose, the fermentable substances; or by
accurately examining the products resulting from fermentation; and it is
evident that the knowledge of either of these must lead to accurate
conclusions concerning the nature and composition of the other. From
these considerations it became necessary accurately to determine the
constituent elements of the fermentable substances; and for this purpose
I did not make use of the compound juices of fruits, the rigorous
analysis of which is perhaps impossible, but made choice of sugar, which
is easily analysed, and the nature of which I have already explained.
This substance is a true vegetable oxyd, with two bases, composed of
hydrogen and carbon, brought to the state of an oxyd by means of a
certain proportion of oxygen; and these three elements are combined in
such a way that a very slight force is sufficient to destroy the
equilibrium of their connection."
After giving the details of his analysis of sugar and of the products of
fermentation, Lavoisier continues:--
"The effect of the vinous fermentation upon sugar is thus reduced to the
mere separation of its elements into two portions; one part is oxygenated
at the expense of the other, so as to form carbonic acid; while the other
part, being disoxygenated in favour of the latter, is converted into the
combustible substance called alkohol; therefore, if it were possible to
re-unite alkohol and carbonic acid together, we ought to form sugar."[1]
[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated by
Robert Kerr. Second Edition, 1793 (pp. 186-196).]
Thus Lavoisier thought he had demonstrated that the carbonic acid and the
alcohol which are produced by the process of fermentation, are equal in
weight to the sugar which disappears; but the application of the more
refined methods of modern chemistry to the investigation of the products
of fermentation by Pasteur, in 1860, proved that this is not exactly
true, and that there is a deficit of from 5 to 7 per cent of the sugar
which is not covered by the alcohol and carbonic acid evolved. The
greater part of this deficit is accounted for by the discovery of two
substances, glycerine and succinic acid, of the existence of which
Lavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent.
still remains to be made good. According to Pasteur, it has been
appropriated by the yeast, but the fact that such appropriation takes
place cannot be said to be actually proved.
However this may be, there can be no doubt that the constituent elements
of fully 98 per cent. of the sugar which has vanished during fermentation
have simply undergone rearrangement; like the soldiers of a brigade, who
at the word of command divide themselves into the independent regiments
to which they belong. The brigade is sugar, the regiments are carbonic
acid, succinic acid, alcohol, and glycerine.
From the time of Fabroni, onwards, it has been admitted that the agent by
which this surprising rearrangement of the particles of the sugar is
effected is the yeast. But the first thoroughly conclusive evidence of
the necessity of yeast for the fermentation of sugar was furnished by
Appert, whose method of preserving perishable articles of food excited so
much attention in France at the beginning of this century. Gay-Lussac, in
his "Mémoire sur la Fermentation,"[2] alludes to Appert's method of
preserving beer-wort unfermented for an indefinite time, by simply
boiling the wort and closing the vessel in which the boiling fluid is
contained, in such a way as thoroughly to exclude air; and he shows that,
if a little yeast be introduced into such wort, after it has cooled, the
wort at once begins to ferment, even though every precaution be taken to
exclude air. And this statement has since received full confirmation from
Pasteur.
[Footnote 2: _Annales de Chimie_, 1810.]
On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amply
proved that air may be allowed to have free access to beer-wort, without
exciting fermentation, if only efficient precautions are taken to prevent
the entry of particles of yeast along with the air.
Thus, the truth that the fermentation of a simple solution of sugar in
water depends upon the presence of yeast, rests upon an unassailable
foundation; and the inquiry into the exact nature of the substance which
possesses such a wonderful chemical influence becomes profoundly
interesting.
The first step towards the solution of this problem was made two
centuries ago by the patient and painstaking Dutch naturalist,
Leeuwenhoek, who in the year 1680 wrote thus:--
"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis per
materiam pellucidam fluitantibus, quarm cerevisiam esse censui, constare
observavi: vidi etiam evidentissime, unumquemque hujus fermenti globulum
denuo ex sex distinctis globulis constare, accurate eidem quantitate et
formae, cui globulis sanguinis nostri, respondentibus.
"Verum talis mihi de horum origine et formatione conceptus formabam;
globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se
constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam
cerevisiam vocare licet, refrigescente, multos ex minimis particulis in
cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae
sexta pars est globuli faecis, et iterum sex ex hisce globulis
conjungi."[3]
[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.]