"La cause du phenomene physique qui accompagne la vie de la plante reside dans un etat physique propre, a.n.a.logue a celui du noir de platine. Mais il est essentiel de remarquer que cet etat physique de la plante est etroitement lie 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 const.i.tution, it is at any rate possible that the physical const.i.tution 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 Thenardian doctrine, supported by Pasteur, according to which the yeast plant a.s.similates 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 elementaires de leurs tissus, comparables aux pet.i.ts 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 ident.i.ty 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 a.n.a.lysis 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 pa.s.sage 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, a.n.a.logous 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 const.i.tuent, 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 pa.s.sages 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 const.i.tuents of living animals is so strongly indicated by Payen. And through the twenty-five years that have pa.s.sed, since the matter of life was first called protoplasm, a host of investigators, among whom Cohn, Max Schulze, and Kuhne must be named as leaders, have acc.u.mulated 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 a.n.a.logous 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 circ.u.mstances, 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 "_Aufklarung_"--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 t.i.tle 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 p.r.o.nounced untenable--nor less untenable (3) the materialism he would found on it."
The paragraph contains three distinct a.s.sertions 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 "_Aufklarung_" 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 quant.i.ty, 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 a.n.a.logy.
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 ma.s.ses 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 a.s.sistant 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 c.o.ke, 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 mult.i.tudes 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 circ.u.mference. 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 ma.s.s of the coal is made up of an acc.u.mulation 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 const.i.tuents: 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 const.i.tutes 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.