Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗

is such a substance); or they may be incapable of living because they have lived, and are products of waste, e. g. urea. The organized substance is a specific combination of organic substances of various kinds, a combination which is organization. Any organized substance is therefore either an independent organism, or part of a more complex organism. Protoplasm, either as a separate organism or as a constituent of a tissue, is organized substance.

Organic substances are numerous and specific. They are various combinations of proximate principles familiar to the chemist, which may conveniently be ranged under three classes: The first class of organic substances comprises those composed of principles having what is called a mineral origin; these generally quit the organism unchanged as they entered it. The second class comprises those which are crystallizable, and are formed in the organism, and generally quit it in this state as excretions. The third class comprises the colloids, i. e. substances which are coagulable and not crystallizable, and are formed in and decomposed in the organism, thus furnishing the principles of the second class. All the principles are in a state of solution. Water is the chief vehicle of the materials which enter and the materials which quit the organism; and bodies in solution are solvents of others, so that the water thus acquires new solvent properties.

45a. Two points must be noted respecting organic substances: they are mostly combinations of higher multiples of the elements; and their combinations are not definite in quantity. Albumen, for example, has (according to one of the many formulas which have been given) an elementary composition of 216 atoms of Carbon, 169 of Hydrogen, 27 of Nitrogen, 3 of Sulphur, and 68 of Oxygen; whereas in its final state, in which it quits the organism as Urea, it is composed of 2 atoms of Carbon, 4 of Hydrogen, 2 of Nitrogen, and 2 of Oxygen, all the Sulphur having disappeared in other combinations. In like manner in the organism Stearin falls from C114, H110, O12, to Oxalic Acid, which is C4, H2, O8. It is obvious that the necessary modifiability of organic substance is due to this multiplicity of its elementary parts and the variety of its molecular structure.

45b. Nor is the indefiniteness of the quantitative composition less important, though seldom adequately appreciated, or even suspected. Robin and Verdeil11 are the only writers I can remember who have distinctly brought the fact into prominence. That all inorganic substances are definite in composition, every one knows. Quicklime, for example, may be got from marble, limestone, oyster-shells, or chalk; but however produced, it always contains exactly 250 ounces of calcium to 100 ounces of oxygen; just as water is always OH2. Not so the pre-eminently vital substances, those which are coagulable and not crystallizable: no precise formula will express one of these; for the same specific substance is found to vary from time to time, and elementary analyses do not give uniform results. Thus, if after causing an acid to combine with one of these substances, we remove the acid, we are not certain of finding the substance as it was before—as we are, for example, after urea is combined with nitric acid and then decomposed. The same want of definiteness is of course even more apparent in the combinations of these proximate principles into organized substance. Protoplasm differs greatly in different places. Epithelial cells differ. Muscular and nervous fibres are never absolutely the same in different regions. A striped and unstriped muscular fibre, the muscular fibre of a sphincter or of a limb, a nerve-fibre in a centre, in a trunk, or in a gland, will present variations of composition. The elastic fibres of the ligaments are larger in the horse than in man; and in other animals they are smaller. These differences are sometimes due to the constituents, and sometimes to the arrangement of the constituents; the conversion of Albumen into Fibrine without elementary loss or addition, is a good example of the latter. That the tissues of one man are not absolutely the same as the tissues of another, in the sense in which it is true to say that the chalk of one hill is the same as that of another, or as gold in Australia is the same as gold in Mexico, is apparent in their very different reactions under similar external conditions: the substance which poisons the one leaves the other unaffected. The man who has once had the small-pox, or scarlet fever, is never the same afterwards, since his organism has now become insusceptible of these poisons. And Sir James Paget has called attention to the striking fact revealed in disease, namely, that in the same tissue—say the bone or the skin—a morbid substance fastens only on certain small portions leaving all the rest unaltered, but fastens on exactly corresponding spots of the opposite sides of the body; so that on both arms, or both legs, only the corresponding bits of tissue will be diseased. “Manifestly when two substances display different relations to a third their composition cannot be identical; so that though we may speak of all bone or of all skin as if it were all alike, yet there are differences of intimate composition. No power of artificial chemistry can detect the difference; but a morbid material can.”12 It is to this variability of composition that we must refer individual peculiarities, and those striking forms of variety known as idiosyncrasies, which cause some organisms to be affected by what seem inexplicable influences—physical and moral.

In spite of all these variations, however, there are certain specific resemblances dependent of course on similarity of composition and structure, so that the muscle of a crustacean is classed beside the muscle of a vertebrate, although the elementary analysis of the two yields different results. Nerve-tissue, according to my experience, is the most variable of all, except the blood; variable not only from individual to individual, and from genus to genus, but even in the same individual it never contains the same quantities of water, phosphates, etc. Hence it is that different nerves manifest different degrees of excitability, and the same nerve differs at different times. Thus the fifth pair, in a poisoned animal, retains its excitability long after the others are paralyzed; and the patient under chloroform feels a prick on the brow or at the temples, when insensible at any other spot. The pneumogastric which is excitable during digestion is—in dogs at least—inexcitable when the animal is fasting.

46. The organic substances are what analysis discovers in organized substances, but none of them, not even the highest, is living, except as organized. Albumen alone, or Stearin alone, is as incapable of Vitality, as Plumbago, or Soda; but all organic substances are capable of playing a part in vital actions; and this part is the more important in proportion to their greater molecular variety. Organization is a special synthesis of substances belonging to all three classes; and the organized substance, thus formed, alone merits the epithet living. We see how organized substances, being constituted by principles derived from the inorganic world, and principles derived from the organic world, have at once a dependence on the external Medium, and an independence of it, which is peculiar to living beings. An analogous dependence and independence is noticeable with respect to the parts; and this is a character not found in inorganic compounds. The organism, even in its simplest forms, is a structure of different substances, each of which is complex. While one part of a crystal is atomically and morphologically identical with every other, and is the whole crystal “writ small,” one part of an organism is unlike another, and no part is like the whole. Hence the dependence of one organ and one tissue on another, and each on all. Yet, while every part is, so to speak, a condition of existence of every other, and the unity of the organism is but the expression of this solidarity,—wherever organized substance has been differentiated into morphological elements (cells, etc.), each of these has its own course of evolution independently of the others,—is born, nourished, developed, and dies.

47. The interdependence of nerve and muscle is seen in this, that the more the muscle is excited the feebler its contractions become; this decrease in contractility is compensated by an increased excitability in its nerve; so that while the muscle demands a more powerful stimulus, the nerve acquires a more energetic activity. Ranke’s curious and careful experiments seem to prove that this depends on the wearied muscle absorbing more water, owing to the acids developed by its activity, and on the nerve losing this water—a nerve being always more irritable when its quantity of water diminishes.

48. Herein we see illustrated the great law of organized activity, that it is a simultaneity of opposite tendencies, as organized matter is a synthesis of compositions and decompositions, always tending towards equilibrium and disturbance, storing up energy and liberating it. Unlike what is observed in unorganized matter, the conditions of waste bring with them conditions of repair, and thus—within certain limits—every loss in one direction is compensated by gain in another. There is a greater flow of nutrient material, or, more properly speaking, a greater assimilation of it by the tissue, where there has been made a greater opening for it by previous disintegration. The alkaline state of the nutrient material, and the acid state of the material that has been used,—the alkaline state which characterizes repose and assimilation, and the acid state which characterizes activity and deassimilation, are but cases of this general law; on the synthesis of these opposite tendencies depends the restless change, together with the continued specific integrity, of organized matter.

49. The state of organization may therefore be defined as the molecular union of the proximate principles of the three classes in reciprocal dissolution. An organism is formed of matter thus organized, which exists in two states—the amorphous and the figured. The amorphous substances are liquid, semi-liquid, and solid; the figured are the cells, fibres, and tubes, called “anatomical elements.” For these I prefer the term suggested, I believe, by Milne Edwards, namely, organites, because they are the individual elements which mainly constitute the organs, and are indeed by many biologists considered as elementary organisms. These organites, which go to form the tissues, and by the tissues the organs, have their specific form, volume, structure, and chemical reactions. They exist in textures or tissues, or separately (e. g. blood corpuscles), and are in many respects like the simplest organisms known, such as Monads, Vibrios, Amœbæ, etc.

50. The simplest form of life is not—as commonly stated—a cell, but a microscopic lump of jelly-like substance, or protoplasm, which has been named sarcode by Dujardin, cytode by Haeckel, and germinal matter by Lionel Beale. This protoplasm, although entirely destitute of texture, and consequently destitute of organs, is nevertheless considered to be living, because it manifests the cardinal phenomena of Life: Assimilation, Evolution, Reproduction, Mobility, and Decay. Examples of this simplest organism are Monads, Protamœbæ, and Polythalamia.13 Few things are more surprising than the vital activity of these organites, which puzzle naturalists as to whether they should be called plants or animals. All microscopists are familiar with the spectacle of a formless lump of albuminous matter (a Rhizopod) putting forth a process of its body as a temporary arm or leg, or else slowly wrapping itself round a microscopic plant, or morsel of animal substance, thus converting its whole body into a mouth and a stomach; but these phenomena are surpassed by those described by Cienkowski,14 who narrates how one Monad fastens on to a plant and sucks the chlorophyll first from one cell and then from another; another Monad, unable to make a hole in the cell-wall, thrusts long