fluid; but he thought that they were merely the starchy particles of the
grain from which the wort was made, rearranged. He discovered the fact
that yeast had a definite structure, but not the meaning of the fact. A
century and a half elapsed, and the investigation of yeast was
recommenced almost simultaneously by Cagniard de la Tour in France, and
by Schwann and Kützing in Germany. The French observer was the first to
publish his results; and the subject received at his hands and at those
of his colleague, the botanist Turpin, full and satisfactory
investigation.
The main conclusions at which they arrived are these. The globular, or
oval, corpuscles which float so thickly in the yeast as to make it muddy,
though the largest are not more than one two-thousandth of an inch in
diameter, and the smallest may measure less than one seven-thousandth of
an inch, are living organisms. They multiply with great rapidity by
giving off minute buds, which soon attain the size of their parent, and
then either become detached or remain united, forming the compound
globules of which Leeuwenhoek speaks, though the constancy of their
arrangement in sixes existed only in the worthy Dutchman's imagination.
It was very soon made out that these yeast organisms, to which Turpin
gave the name of _Torula cerevisioe_, were more nearly allied to the
lower Fungi than to anything else. Indeed Turpin, and subsequently
Berkeley and Hoffmann, believed that they had traced the development of
the _Torula_ into the well-known and very common mould--the _Penicillium
glaucum_. Other observers have not succeeded in verifying these
statements; and my own observations lead me to believe, that while the
connection between _Torula_ and the moulds is a very close one, it is of
a different nature from that which has been supposed. I have never been
able to trace the development of _Torula_ into a true mould; but it is
quite easy to prove that species of true mould, such as _Penicillium_,
when sown in an appropriate nidus, such as a solution of tartrate of
ammonia and yeast-ash, in water, with or without sugar, give rise to
_Toruloe_, similar in all respects to _T. cerevisioe_, except that they
are, on the average, smaller. Moreover, Bail has observed the development
of a _Torula_ larger than _T. cerevisioe_, from a _Mucor_, a mould allied
to _Penicillium_.
It follows, therefore, that the _Toruloe_, or organisms of yeast, are
veritable plants; and conclusive experiments have proved that the power
which causes the rearrangement of the molecules of the sugar is
intimately connected with the life and growth of the plant. In fact,
whatever arrests the vital activity of the plant also prevents it from
exciting fermentation.
Such being the facts with regard to the nature of yeast, and the changes
which it effects in sugar, how are they to be accounted for? Before
modern chemistry had come into existence, Stahl, stumbling, with the
stride of genius, upon the conception which lies at the bottom of all
modern views of the process, put forward the notion that the ferment,
being in a state of internal motion, communicated that motion to the
sugar, and thus caused its resolution into new substances. And Lavoisier,
as we have seen, adopts substantially the same view. But Fabroni, full of
the then novel conception of acids and bases and double decompositions,
propounded the hypothesis that sugar is an oxide with two bases, and the
ferment a carbonate with two bases; that the carbon of the ferment unites
with the oxygen of the sugar, and gives rise to carbonic acid; while the
sugar, uniting with the nitrogen of the ferment, produces a new substance
analogous to opium. This is decomposed by distillation, and gives rise to
alcohol. Next, in 1803, Thénard propounded a hypothesis which partakes
somewhat of the nature of both Stahl's and Fabroni's views. "I do not
believe with Lavoisier," he says, "that all the carbonic acid formed
proceeds from the sugar. How, in that case, could we conceive the action
of the ferment on it? I think that the first portions of the acid are due
to a combination of the carbon of the ferment with the oxygen of the
sugar, and that it is by carrying off a portion of oxygen from the last
that the ferment causes the fermentation to commence--the equilibrium
between the principles of the sugar being disturbed, they combine afresh
to form carbonic acid and alcohol."
The three views here before us may be familiarly exemplified by supposing
the sugar to be a card-house. According to Stahl, the ferment is somebody
who knocks the table, and shakes the card-house down; according to
Fabroni, the ferment takes out some cards, but puts others in their
places; according to Thénard, the ferment simply takes a card out of the
bottom story, the result of which is that all the others fall.
As chemistry advanced, facts came to light which put a new face upon
Stahl's hypothesis, and gave it a safer foundation than it previously
possessed. The general nature of these phenomena may be thus stated:--A
body, A, without giving to, or taking from, another body B, any material
particles, causes B to decompose into other substances, C, D, E, the sum
of the weights of which is equal to the weight of B, which decomposes.
Thus, bitter almonds contain two substances, amygdalin and synaptase,
which can be extracted, in a separate state, from the bitter almonds. The
amygdalin thus obtained, if dissolved in water, undergoes no change; but
if a little synaptase be added to the solution, the amygdalin splits up
into bitter almond oil, prussic acid, and a kind of sugar.
A short time after Cagniard de la Tour discovered the yeast plant,
Liebig, struck with the similarity between this and other such processes
and the fermentation of sugar, put forward the hypothesis that yeast
contains a substance which acts upon sugar, as synaptase acts upon
amygdalin. And as the synaptase is certainly neither organized nor alive,
but a mere chemical substance, Liebig treated Cagniard de la Tour's
discovery with no small contempt, and, from that time to the present, has
steadily repudiated the notion that the decomposition of the sugar is, in
any sense, the result of the vital activity of the _Torula_. But, though
the notion that the _Torula_ is a creature which eats sugar and excretes
carbonic acid and alcohol, which is not unjustly ridiculed in the most
surprising paper that ever made its appearance in a grave scientific
journal,[4] may be untenable, the fact that the _Toruloe_ are alive, and
that yeast does not excite fermentation unless it contains living
_Toruloe_, stands fast. Moreover, of late years, the essential
participation of living organisms in fermentation other than the
alcoholic, has been clearly made out by Pasteur and other chemists.
[Footnote 4: "Das enträthselte Geheimniss der geistigen Gährung
(Vorlänfige briefliche Mittheilung)" is the title of an anonymous
contribution to Wöhler and Liebig's _Annalen der Pharmacie_ for 1839, in
which a somewhat Rabelaisian imaginary description of the organisation of
the "yeast animals" and of the manner in which their functions are
performed, is given with a circumstantiality worthy of the author of
_Gulliver's Travels_. As a specimen of the writer's humour, his account
of what happens when fermentation comes to an end may suffice. "Sobald
nämlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich
gegenseitig selbst auf, was durch eine eigene Manipulation geschieht;
alles wird verdant bis auf die Eier, welche unverändert durch den
Darmkanal hineingehen; man hat zuletzt wieder gährungsfähige Hefe,
nämlich den Saamen der Thiere, der übrig bleibt."] However, it may be
asked, is there any necessary opposition between the so-called "vital"
and the strictly physico-chemical views of fermentation? It is quite
possible that the living _Torula_ may excite fermentation in sugar,
because it constantly produces, as an essential part of its vital
manifestations, some substance which acts upon the sugar, just as the
synaptase acts upon the amygdalin. Or it may be, that, without the
formation of any such special substance, the physical condition of the
living tissue of the yeast plant is sufficient to effect that small
disturbance of the equilibrium of the particles of the sugar, which
Lavoisier thought sufficient to effect its decomposition.
Platinum in a very fine state of division--known as platinum black, or
_noir de platine_--has the very singular property of causing alcohol to
change into acetic acid with great rapidity. The vinegar plant, which is
closely allied to the yeast plant, has a similar effect upon dilute
alcohol, causing it to absorb the oxygen of the air, and become converted
into vinegar; and Liebig's eminent opponent, Pasteur, who has done so
much for the theory and the practice of vinegar-making, himself suggests
that in this case--
"La cause du phénomène physique qui accompagne la vie de la plante réside
dans un état physique propre, analogue à celui du noir de platine. Mais
il est essentiel de remarquer que cet état physique de la plante est
étroitement lié avec la vie de cette plante."[5]
[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.]
Now, if the vinegar plant gives rise to the oxidation of alcohol, on
account of its merely physical constitution, it is at any rate possible
that the physical constitution of the yeast plant may exert a decomposing
influence on sugar.
But, without presuming to discuss a question which leads us into the very
arcana of chemistry, the present state of speculation upon the _modus
operandi_ of the yeast plant in producing fermentation is represented, on
the one hand, by the Stahlian doctrine, supported by Liebig, according to
which the atoms of the sugar are shaken into new combinations either
directly by the _Toruloe_, or indirectly, by some substance formed by
them; and, on the other hand, by the Thénardian doctrine, supported by
Pasteur, according to which the yeast plant assimilates part of the
sugar, and, in so doing, disturbs the rest, and determines its resolution
into the products of fermentation. Perhaps the two views are not so much
opposed as they seem at first sight to be.
But the interest which attaches to the influence of the yeast plants upon
the medium in which they live and grow does not arise solely from its
bearing upon the theory of fermentation. So long ago as 1838, Turpin
compared the _Toruloe_ to the ultimate elements of the tissues of animals
and plants--"Les organes élémentaires de leurs tissus, comparables aux
petits végétaux des levures ordinaires, sont aussi les décompositeurs des
substances qui les environnent."
Almost at the same time, and, probably, equally guided by his study of
yeast, Schwann was engaged in those remarkable investigations into the
form and development of the ultimate structural elements of the tissues
of animals, which led him to recognise their fundamental identity with
the ultimate structural elements of vegetable organisms.
The yeast plant is a mere sac, or "cell," containing a semi-fluid matter,
and Schwann's microscopic analysis resolved all living organisms, in the
long run, into an aggregation of such sacs or cells, variously modified;
and tended to show, that all, whatever their ultimate complication, begin
their existence in the condition of such simple cells.
In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_
as a "cell"; and, in a remarkable note to the passage in which he refers
to the yeast plant, Schwann says:--
"I have been unable to avoid mentioning fermentation, because it is the
most fully and exactly known operation of cells, and represents, in the
simplest fashion, the process which is repeated by every cell of the
living body."
In other words, Schwann conceives that every cell of the living body
exerts an influence on the matter which surrounds and permeates it,
analogous to that which a _Torula_ exerts on the saccharine solution by
which it is bathed. A wonderfully suggestive thought, opening up views of
the nature of the chemical processes of the living body, which have
hardly yet received all the development of which they are capable.
Kant defined the special peculiarity of the living body to be that the
parts exist for the sake of the whole and the whole for the sake of the
parts. But when Turpin and Schwann resolved the living body into an
aggregation of quasi-independent cells, each, like a _Torula_, leading
its own life and having its own laws of growth and development, the
aggregation being dominated and kept working towards a definite end only
by a certain harmony among these units, or by the superaddition of a
controlling apparatus, such as a nervous system, this conception ceased
to be tenable. The cell lives for its own sake, as well as for the sake
of the whole organism; and the cells which float in the blood, live at
its expense, and profoundly modify it, are almost as much independent
organisms as the _Toruloe_ which float in beer-wort.
Schwann burdened his enunciation of the "cell theory" with two false
suppositions; the one, that the structures he called "nucleus"[6] and
"cell-wall" are essential to a cell; the other, that cells are usually
formed independently of other cells; but, in 1839, it was a vast and
clear gain to arrive at the conception, that the vital functions of all
the higher animals and plants are the resultant of the forces inherent in
the innumerable minute cells of which they are composed, and that each of
them is, itself, an equivalent of one of the lowest and simplest of
independent living beings--the _Torula_.
[Footnote 6: Later investigations have thrown an entirely new light upon
the structure and the functional importance of the nucleus; and have
proved that Schwann did not over-estimate its importance. 1894.]
From purely morphological investigations, Turpin and Schwann, as we have
seen, arrived at the notion of the fundamental unity of structure of
living beings. And, before long, the researches of chemists gradually led
up to the conception of the fundamental unity of their composition.
So far back as 1803, Thénard pointed out, in most distinct terms, the
important fact that yeast contains a nitrogenous "animal" substance; and
that such a substance is contained in all ferments. Before him, Fabroni
and Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulder
endeavoured to demonstrate that a peculiar substance, which he called
"protein," was essentially characteristic of living matter.
In 1846, Payen writes:--
"Enfin, une loi sans exception me semble apparaître dans les faits
nombreux que j'ai observés et conduire à envisager sous un nouveau jour
la vie végétale; si je ne m'abuse, tout ce que dans les tissus végétaux
la vue directe où amplifiée nous permet de discerner sous la forme de
cellules et de vaisseaux, ne représente autre chose que les enveloppes
protectrices, les réservoirs et les conduits, à l'aide desquels les corps
animés qui les secrètent et les façonnent, se logent, puisent et
charrient leurs aliments, déposent et isolent les matières excrétées."
And again:--
"Afin de compléter aujourd'hui l'énoncé du fait général, je rappellerai
que les corps, doué des fonctions accomplies dans les tissus des plantes,
sont formés des éléments qui constituent, en proportion peu variable, les
organismes animaux; qu'ainsi l'on est conduit à reconnaître une immense
unité de composition élémentaire dans tous les corps vivants de la
nature."[7]
[Footnote 7: Mém. sur les Développements des Végétaux, &c.--_Mém.
Présentées_. ix. 1846.]
In the year (1846) in which these remarkable passages were published, the
eminent German botanist, Von Mohl invented the word "protoplasm," as a
name for one portion of those nitrogenous contents of the cells of living
plants, the close chemical resemblance of which to the essential
constituents of living animals is so strongly indicated by Payen. And
through the twenty-five years that have passed, since the matter of life
was first called protoplasm, a host of investigators, among whom Cohn,
Max Schulze, and Kühne must be named as leaders, have accumulated
evidence, morphological, physiological, and chemical, in favour of that
"immense unité de composition élémentaire dans tous les corps vivants de
la nature," into which Payen had, so early, a clear insight.
As far back as 1850, Cohn wrote, apparently without any knowledge of what
Payen had said before him:--
"The protoplasm of the botanist, and the contractile substance and
sarcode of the zoologist, must be, if not identical, yet in a high degree
analogous substances. Hence, from this point of view, the difference
between animals and plants consists in this; that, in the latter, the
contractile substance, as a primordial utricle, is enclosed within an
inert cellulose membrane, which permits it only to exhibit an internal
motion, expressed by the phenomena of rotation and circulation, while, in
the former, it is not so enclosed. The protoplasm in the form of the
primordial utricle is, as it were, the animal element in the plant, but
which is imprisoned, and only becomes free in the animal; or, to strip
off the metaphor which obscures simple thought, the energy of organic
vitality which is manifested in movement is especially exhibited by a
nitrogenous contractile substance, which in plants is limited and
fettered by an inert membrane, in animals not so."[8]
[Footnote 8: Cohn, "Ueber Protococcus pluvialis," in the _Nova Acta_ for
1850.]
In 1868, thinking that an untechnical statement of the views current
among the leaders of biological science might be interesting to the
general public, I gave a lecture embodying them in Edinburgh. Those who
have not made the mistake of attempting to approach biology, either by
the high _à priori_ road of mere philosophical speculation, or by the
mere low _à posteriori_ lane offered by the tube of a microscope, but
have taken the trouble to become acquainted with well-ascertained facts
and with their history, will not need to be told that in what I had to
say "as regards protoplasm" in my lecture "On the Physical Basis of Life"
(Vol. I. of these Essays, p. 130), there was nothing new; and, as I hope,
nothing that the present state of knowledge does not justify us in
believing to be true. Under these circumstances, my surprise may be
imagined, when I found, that the mere statement of facts and of views,
long familiar to me as part of the common scientific property of
Continental workers, raised a sort of storm in this country, not only by
exciting the wrath of unscientific persons whose pet prejudices they
seemed to touch, but by giving rise to quite superfluous explosions on
the part of some who should have been better informed.
Dr. Stirling, for example, made my essay the subject of a special
critical lecture,[9] which I have read with much interest, though, I
confess, the meaning of much of it remains as dark to me as does the
"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr.
Stirling's method of dealing with the subject is peculiar. "Protoplasm"
is a question of history, so far as it is a name; of fact, so far as it
is a thing. Dr. Stirling, has not taken the trouble to refer to the
original authorities for his history, which is consequently a travesty;
and still less has he concerned himself with looking at the facts, but
contents himself with taking them also at second-hand. A most amusing
example of this fashion of dealing with scientific statements is
furnished by Dr. Stirling's remarks upon my account of the protoplasm of
the nettle hair. That account was drawn up from careful and often-
repeated observation of the facts. Dr. Stirling thinks he is offering a
valid criticism, when he says that my valued friend Professor Stricker
gives a somewhat different statement about protoplasm. But why in the
world did not this distinguished Hegelian look at a nettle hair for
himself, before venturing to speak about the matter at all? Why trouble
himself about what either Stricker or I say, when any tyro can see the
facts for himself, if he is provided with those not rare articles, a
nettle and a microscope? But I suppose this would have been
"_Aufklärung_"--a recurrence to the base common-sense philosophy of the
eighteenth century, which liked to see before it believed, and to
understand before it criticised Dr. Stirling winds up his paper with the
following paragraph:--
[Footnote 9: Subsequently published under the title of "As regards
Protoplasm."]
"In short, the whole position of Mr. Huxley, (1) that all organisms
consist alike of the same life-matter, (2) which life-matter is, for its
part, due only to chemistry, must be pronounced untenable--nor less
untenable (3) the materialism he would found on it."
The paragraph contains three distinct assertions concerning my views, and
just the same number of utter misrepresentations of them. That which I
have numbered (1) turns on the ambiguity of the word "same," for a
discussion of which I would refer Dr. Stirling to a great hero of
"_Aufklärung_" Archbishop Whately; statement number (2) is, in my
judgment, absurd, and certainly I have never said anything resembling it;
while, as to number (3), one great object of my essay was to show that
what is called "materialism" has no sound philosophical basis!
As we have seen, the study of yeast has led investigators face to face
with problems of immense interest in pure chemistry, and in animal and
vegetable morphology. Its physiology is not less rich in subjects for
inquiry. Take, for example, the singular fact that yeast will increase
indefinitely when grown in the dark, in water containing only tartrate of
ammonia a small percentage of mineral salts and sugar. Out of these
materials the _Toruloe_ will manufacture nitrogenous protoplasm,
cellulose, and fatty matters, in any quantity, although they are wholly
deprived of those rays of the sun, the influence of which is essential to
the growth of ordinary plants. There has been a great deal of speculation
lately, as to how the living organisms buried beneath two or three
thousand fathoms of water, and therefore in all probability almost
deprived of light, live. If any of them possess the same powers as yeast
(and the same capacity for living without light is exhibited by some
other fungi) there would seem to be no difficulty about the matter.
Of the pathological bearings of the study of yeast, and other such
organisms, I have spoken elsewhere. It is certain that, in some animals,
devastating epidemics are caused by fungi of low order--similar to those
of which _Torula_ is a sort of offshoot. It is certain that such diseases
are propagated by contagion and infection, in just the same way as
ordinary contagious and infectious diseases are propagated. Of course, it
does not follow from this, that all contagious and infectious diseases
are caused by organisms of as definite and independent a character as the
_Torula_; but, I think, it does follow that it is prudent and wise to
satisfy one's self in each particular case, that the "germ theory" cannot
and will not explain the facts, before having recourse to hypotheses
which have no equal support from analogy.
V
ON THE FORMATION OF COAL
[1870]
The lumps of coal in a coal-scuttle very often have a roughly cubical
form. If one of them be picked out and examined with a little care, it
will be found that its six sides are not exactly alike. Two opposite
sides are comparatively smooth and shining, while the other four are much
rougher, and are marked by lines which run parallel with the smooth
sides. The coal readily splits along these lines, and the split surfaces
thus formed are parallel with the smooth faces. In other words, there is
a sort of rough and incomplete stratification in the lump of coal, as if
it were a book, the leaves of which had stuck together very closely.