Critiques and Addresses by Thomas Henry Huxley

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Dr. Stirling, for example, made my essay the subject of a special
critical lecture[1], 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
secondhand. 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 "_Aufklaerung_"--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 1: 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 "_Aufklaerung_", 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 _Torulae_ 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 oneself 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.

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.

Sometimes the faces along which the coal splits are not smooth, but
exhibit a thin layer of dull, charred-looking substance, which is
known as "mineral charcoal."

Occasionally one of the faces of a lump of coal will present
impressions, which are obviously those of the stem, or leaves, of a
plant; but though hard mineral masses of pyrites, and even fine mud,
may occur here and there, neither sand nor pebbles are met with.

When the coal burns, the chief ultimate products of its combustion
are carbonic acid, water, and ammoniacal products, which escape up the
chimney; and a greater or less amount of residual earthy salts, which
take the form of ash. These products are, to a great extent, such as
would result from the burning of so much wood.

These properties of coal may be made out without any very refined
appliances, but the microscope reveals something more. Black and
opaque as ordinary coal is, slices of it become transparent if they
are cemented in Canada balsam, and rubbed down very thin, in the
ordinary way of making thin sections of non-transparent bodies. But
as the thin slices, made in this way, are very apt to crack and break
into fragments, it is better to employ marine glue as the cementing
material. By the use of this substance, slices of considerable size
and of extreme thinness and transparency may be obtained.[1]

[Footnote 1: My assistant in the Museum of Practical Geology, Mr.
Newton, invented this excellent method of obtaining thin slices of
coal.]

Now let us suppose two such slices to be prepared from our lump of
coal--one parallel with the bedding, the other perpendicular to it;
and let us call the one the horizontal, and the other the vertical,
section. The horizontal section will present more or less rounded
yellow patches and streaks, scattered irregularly through the dark
brown, or blackish, ground substance; while the vertical section will
exhibit more elongated bars and granules of the same yellow materials,
disposed in lines which correspond, roughly, with the general
direction of the bedding of the coal.

This is the microscopic structure of an ordinary piece of coal. But if
a great series of coals, from different localities and seams, or even
from different parts of the same seam, be examined, this structure
will be found to vary in two directions. In the anthracitic, or
stone-coals, which burn like coke, the yellow matter diminishes, and
the ground substance becomes more predominant, and blacker, and more
opaque, until it becomes impossible to grind a section thin enough to
be translucent; while, on the other hand, in such as the "Better-Bed"
coal of the neighbourhood of Bradford, which burns with much flame,
the coal is of a far lighter colour, and transparent sections are very
easily obtained. In the browner parts of this coal, sharp eyes will
readily detect multitudes of curious little coin-shaped bodies, of a
yellowish brown colour, embedded in the dark brown ground substance.
On the average, these little brown bodies may have a diameter of about
one-twentieth of an inch. They lie with their flat surfaces nearly
parallel with the two smooth faces of the block in which they are
contained; and, on one side of each, there may be discerned a figure,
consisting of three straight linear marks, which radiate from the
centre of the disk, but do not quite reach its circumference. In the
horizontal section these disks are often converted into more or less
complete rings; while in the vertical sections they appear like thick
hoops, the sides of which have been pressed together. The disks are,
therefore, flattened bags; and favourable sections show that the
three-rayed marking is the expression of three clefts, which penetrate
one wall of the bag.

The sides of the bags are sometimes closely approximated; but, when
the bags are less flattened, their cavities are, usually, filled with
numerous, irregularly rounded, hollow bodies, having the same kind of
wall as the large ones, but not more than one seven-hundredth of an
inch in diameter.

In favourable specimens, again, almost the whole ground substance
appears to be made up of similar bodies--more or less carbonized
or blackened--and, in these, there can be no doubt that, with the
exception of patches of mineral charcoal, here and there, the whole
mass of the coal is made up of an accumulation of the larger and of
the smaller sacs.

But, in one and the same slice, every transition can be observed from
this structure to that which has been described as characteristic of
ordinary coal. The latter appears to rise out of the former, by the
breaking-up and increasing carbonization of the larger and the smaller
sacs. And, in the anthracitic coals, this process appears to have gone
to such a length, as to destroy the original structure altogether, and
to replace it by a completely carbonized substance.

Thus coal may be said, speaking broadly, to be composed of two
constituents: firstly, mineral charcoal; and, secondly, coal proper.
The nature of the mineral charcoal has long since been determined. Its
structure shows it to consist of the remains of the stems and leaves
of plants, reduced to little more than their carbon. Again, some of
the coal is made up of the crushed and flattened bark, or outer coat,
of the stems of plants, the inner wood of which has completely decayed
away. But what I may term the "saccular matter" of the coal, which,
either in its primary or in its degraded form, constitutes by far the
greater part of all the bituminous coals I have examined, is certainly
not mineral charcoal; nor is its structure that of any stem or leaf.
Hence its real nature is, at first, by no means apparent, and has been
the subject of much discussion.

The first person who threw any light upon the problem, as far as I
have been able to discover, was the well-known geologist, Professor
Morris. It is now thirty-four years since he carefully described and
figured the coin-shaped bodies, or larger sacs, as I have called
them, in a note appended to the famous paper "On the Coal-brookdale
Coal-Field," published at that time, by the present President of
the Geological Society, Mr. Prestwich. With much sagacity, Professor
Morris divined the real nature of these bodies, and boldly
affirmed them to be the spore-cases of a plant allied to the living
club-mosses.

But discovery sometimes makes a long halt; and it is only a few
years since Mr. Carruthers determined the plant (or rather one of the
plants) which produces these spore-cases, by finding the discoidal
sacs still adherent to the leaves of the fossilized cone which
produced them. He gave the name of _Flemingites gracilis_ to the plant
of which the cones form a part. The branches and stem of this plant
are not yet certainly known, but there is no sort of doubt that it was
closely allied to the _Lepidodendron_, the remains of which abound in
the coal formation. The _Lepidodendra_ were shrubs and trees which put
one more in mind of an _Araucaria_ than of any other familiar plant;
and the ends of the fruiting branches were terminated by cones, or
catkins, somewhat like the bodies so named in a fir, or a willow.
These conical fruits, however, did not produce seeds; but the leaves
of which they were composed bore upon their surfaces sacs full of
spores or sporangia, such as those one sees on the under surface of a
bracken leaf. Now, it is these sporangia of the Lepidodendroid plant
_Flemingites_ which were identified by Mr. Carruthers with the free
sporangia described by Professor Morris, which are the same as the
large sacs of which I have spoken. And, more than this, there is
no doubt that the small sacs are the spores, which were originally
contained in the sporangia.

The living club-mosses are, for the most part, insignificant and
creeping herbs, which, superficially, very closely resemble true
mosses, and none of them reach more than two or three feet in height.
But, in their essential structure, they very closely resemble the
earliest Lepidodendroid trees of the coal: their stems and leaves are
similar; so are their cones; and no less like are the sporangia and
spores; while even in their size, the spores of the _Lepidodendron_
and those of the existing _Lycopodium_, or club-moss, very closely
approach one another.

Thus, the singular conclusion is forced upon us, that the greater and
the smaller sacs of the "Better-Bed" and other coals, in which the
primitive structure is well preserved, are simply the sporangia and
spores of certain plants, many of which were closely allied to the
existing club-mosses. And if, as I believe, it can be demonstrated
that ordinary coal is nothing but "saccular" coal which has undergone
a certain amount of that alteration which, if continued, would convert
it into anthracite; then, the conclusion is obvious, that the great
mass of the coal we burn is the result of the accumulation of the
spores and spore-cases of plants, other parts of which have furnished
the carbonized stems and the mineral charcoal, or have left their
impressions on the surfaces of the layer.

Of the multitudinous speculations which, at various times, have been
entertained respecting the origin and mode of formation of coal,
several appear to be negatived, and put out of court, by the
structural facts the significance of which I have endeavoured to
explain. These facts, for example, do not permit us to suppose that
coal is an accumulation of peaty matter, as some have held.

Again, the late Professor Quekett was one of the first observers
who gave a correct description of what I have termed the "saccular"
structure of coal; and, rightly perceiving that this structure was
something quite different from that of any known plant, he imagined
that it proceeded from some extinct vegetable organism which was
peculiarly abundant amongst the coal-forming plants. But this
explanation is at once shown to be untenable when the smaller and the
larger sacs are proved to be spores or sporangia.

Some, once more, have imagined that coal was of submarine origin; and
though the notion is amply and easily refuted by other considerations,
it may be worth while to remark, that it is impossible to comprehend
how a mass of light and resinous spores should have reached the bottom
of the sea, or should have stopped in that position if they had got
there.

At the same time, it is proper to remark that I do not presume to
suggest that all coal must needs have the same structure; or that
there may not be coals in which the proportions of wood and spores, or
spore-cases, are very different from those which I have examined. All
I repeat is, that none of the coals which have come under my notice
have enabled me to observe such a difference. But, according to
Principal Dawson, who has so sedulously examined the fossil remains of
plants in North America, it is otherwise with the vast accumulations
of coal in that country.

"The true coal," says Dr. Dawson, "consists principally of
the flattened bark of Sigillarioid and other trees, intermixed
with leaves of Ferns and _Cordaites_, and other herbaceous
_debris_, and with fragments of decayed wood, constituting
'mineral charcoal,' all these materials having manifestly
alike grown and accumulated where we find them."[1]

[Footnote 1: "Acadian Geology," 2nd edition, p. 138.]

When I had the pleasure of seeing Principal Dawson in London last
summer, I showed him my sections of coal, and begged him to re-examine
some of the American coals on his return to Canada, with an eye to the
presence of spores and sporangia, such as I was able to show him in
our English and Scotch coals. He has been good enough to do so; and in
a letter dated September 26th, 1870, he informs me that--

"Indications of spore-cases are rare, except in certain coarse
shaly coals and portions of coals, and in the roofs of the
seams. The most marked case I have yet met with is the shaly
coal referred to as containing _Sporangites_ in my paper
on the conditions of accumulation of coal (_Journal of the
Geological Society_, vol. xxii. pp. 115, 139, and 165). The
purer coals certainly consist principally of cubical tissues
with some true woody matter, and the spore-cases, &c.,
are chiefly in the coarse and shaly layers. This is my old
doctrine in my two papers in the _Journal of the Geological
Society_, and I see nothing to modify it. Your observations,
however, make it probable that the frequent _clear spots_ in
the cannels are spore-cases."

Dr. Dawson's results are the more remarkable, as the numerous
specimens of British coal, from various localities, which I have
examined, tell one tale as to the predominance of the spore and
sporangium element in their composition; and as it is exactly in the
finest and purest coals, such as the "Better-Bed" coal of Lowmoor,
that the spores and sporangia obviously constitute almost the entire
mass of the deposit.

Coal, such as that which has been described, is always found in
sheets, or "seams," varying from a fraction of an inch to many feet
in thickness, enclosed in the substance of the earth at very various
depths, between beds of rock of different kinds. As a rule, every seam
of coal rests upon a thicker, or thinner, bed of clay, which is known
as "under-clay." These alternations of beds of coal, clay, and rock
may be repeated many times, and are known as the "coal-measures;"
and in some regions, as in South Wales and in Nova Scotia, the
coal-measures attain a thickness of twelve or fourteen thousand
feet, and enclose eighty or a hundred seams of coal, each with its
under-clay, and separated from those above and below by beds of
sandstone and shale.

The position of the beds which constitute the coal-measures is
infinitely diverse. Sometimes they are tilted up vertically, sometimes
they are horizontal, sometimes curved into great basins; sometimes
they come to the surface, sometimes they are covered up by thousands
of feet of rock. But, whatever their present position, there is
abundant and conclusive evidence that every under-clay was once a
surface soil. Not only do carbonized root-fibres frequently abound in
these under-clays; but the stools of trees, the trunks of which are
broken off and confounded with the bed of coal, have been repeatedly
found passing into radiating roots, still embedded in the under-clay.
On many parts of the coast of England, what are commonly known as
"submarine forests" are to be seen at low water. They consist, for the
most part, of short stools of oak, beech, and fir trees, still fixed
by their long roots in the bed of blue clay in which they originally
grew. If one of these submarine forest beds should be gradually
depressed and covered up by new deposits, it would present just the
same characters as an under-clay of the coal, if the _Sigillaria_ and
_Lepidodendron_ of the ancient world were substituted for the oak, or
the beech, of our own times.

In a tropical forest, at the present day, the trunks of fallen trees,
and the stools of such trees as may have been broken by the violence
of storms, remain entire for but a short time. Contrary to what might
be expected, the dense wood of the tree decays, and suffers from the
ravages of insects, more swiftly than the bark. And the traveller,
setting his foot on a prostrate trunk, finds that it is a mere shell,
which breaks under his weight, and lands his foot amidst the insects,
or the reptiles, which have sought food or refuge within.

The trees of the coal forests present parallel conditions. When the
fallen trunks which have entered into the composition of the bed of
coal are identifiable, they are mere double shells of bark, flattened
together in consequence of the destruction of the woody core; and Sir
Charles Lyell and Principal Dawson discovered, in the hollow stools
of coal trees of Nova Scotia, the remains of snails, millipedes,
and salamander-like creatures, embedded in a deposit of a different
character from that which surrounded the exterior of the trees. Thus,
in endeavouring to comprehend the formation of a seam of coal, we must
try to picture to ourselves a thick forest, formed for the most part
of trees like gigantic club-mosses, mares-tails, and tree ferns, with
here and there some that had more resemblance to our existing yews and
fir-trees. We must suppose that, as the seasons rolled by, the plants
grew and developed their spores and seeds; that they shed these in
enormous quantities, which accumulated on the ground beneath; and
that, every now and then, they added a dead frond or leaf; or, at
longer intervals, a rotten branch, or a dead trunk, to the mass.

A certain proportion of the spores and seeds no doubt fulfilled their
obvious function, and, carried by the wind to unoccupied regions,
extended the limits of the forest; many might be washed away by rain
into streams, and be lost; but a large portion must have remained, to
accumulate like beech-mast, or acorns, beneath the trees of a modern
forest.

But, in this case, it may be asked, why does not our English coal
consist of stems and leaves to a much greater extent than it does?
What is the reason of the predominance of the spores and spore-cases
in it?

A ready answer to this question is afforded by the study of a living
full-grown club-moss. Shake it upon a piece of paper, and it emits a
cloud of fine dust, which falls over the paper, and is the well-known
Lycopodium powder. Now this powder used to be, and I believe still
is, employed for two objects, which seem at first sight to have no
particular connection with one another. It is, or was, employed in
making lightning, and in making pills. The coats of the spores contain
so much resinous matter, that a pinch of Lycopodium powder, thrown
through the flame of a candle, burns with an instantaneous flash,
which has long done duty for lightning on the stage. And the same
character makes it a capital coating for pills; for the resinous
powder prevents the drug from being wetted by the saliva, and thus
bars the nauseous flavour from the sensitive papillae of the tongue.

But this resinous matter, which lies in the walls of the spores and
sporangia, is a substance not easily altered by air and water,
and hence tends to preserve these bodies, just as the bituminized
cerecloth preserves an Egyptian mummy; while, on the other hand, the
merely woody stem and leaves tend to rot, as fast as the wood of the
mummy's coffin has rotted. Thus the mixed heap of spores, leaves,
and stems in the coal-forest would be persistently searched by the
long-continued action of air and rain; the leaves and stems would
gradually be reduced to little but their carbon, or, in other words,
to the condition of mineral charcoal in which we find them; while the
spores and sporangia remained as a comparatively unaltered and compact
residuum.

There is, indeed, tolerably clear evidence that the coal must, under
some circumstances, have been converted into a substance hard enough
to be rolled into pebbles, while it yet lay at the surface of the
earth; for in some seams of coal, the courses of rivulets, which must
have been living water, while the stratum in which their remains are
found was still at the surface, have been observed to contain rolled
pebbles of the very coal through which the stream has cut its way.

The structural facts are such as to leave no alternative but to adopt
the view of the origin of such coal as I have described, which has
just been stated; but, happily, the process is not without analogy at
the present day. I possess a specimen of what is called "white coal"
from Australia. It is an inflammable material, burning with a bright
flame, and having much the consistence and appearance of oat-cake,
which, I am informed, covers a considerable area. It consists, almost
entirely, of a compacted mass of spores and spore-cases. But the fine
particles of blown sand which are scattered through it, show that it
must have accumulated, subaerially, upon the surface of a soil covered
by a forest of cryptogamous plants, probably tree-ferns.

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