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 _Torulae_ 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" 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._
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 charriant leurs aliments, déposent et isolent les matières
excrétées."
And again:--
"A fin de complêter 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."[1]
[Footnote 1: "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."[1]
[Footnote 1: 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," 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[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 "_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 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 "_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 _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
_débris_, 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--