Discourses - Thomas H. Huxley
Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23
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 elementaires de leurs tissus, comparables aux
petits vegetaux des levures ordinaires, sont aussi les decompositeurs 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, Thenard 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 apparaitre dans les faits
nombreux que j'ai observes et conduire a envisager sous un nouveau jour
la vie vegetale; si je ne m'abuse, tout ce que dans les tissus vegetaux
la vue directe ou amplifiee nous permet de discerner sous la forme de
cellules et de vaisseaux, ne represente autre chose que les enveloppes
protectrices, les reservoirs et les conduits, a l'aide desquels les corps
animes qui les secretent et les faconnent, se logent, puisent et
charrient leurs aliments, deposent et isolent les matieres excretees."
And again:--
"Afin de completer aujourd'hui l'enonce du fait general, je rappellerai
que les corps, doue des fonctions accomplies dans les tissus des plantes,
sont formes des elements qui constituent, en proportion peu variable, les
organismes animaux; qu'ainsi l'on est conduit a reconnaitre une immense
unite de composition elementaire dans tous les corps vivants de la
nature."[7]
[Footnote 7: Mem. sur les Developpements des Vegetaux, &c.--_Mem.
Presentees_. 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 Kuehne must be named as leaders, have accumulated
evidence, morphological, physiological, and chemical, in favour of that
"immense unite de composition elementaire 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 _a priori_ road of mere philosophical speculation, or by the
mere low _a 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
"_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 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
"_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 _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.
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 mere 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, 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 a 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 Coalbrookdale 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."[2]
[Footnote 2: _Acadian Geology_, 2nd edition, p. 135.]