Popular Science Monthly/Volume 21/July 1882/Protoplasm
| PROTOPLASM. |
By FRANCES EMILY WHITE, M.D.[1]
AT the recent International Medical Congress, held in London, upon which the attention and enthusiastic interest of the whole medical world were for the time being centered, Professor Huxley, in an address made to that assembly, used the term "medicine" to include "the great body of theoretical and practical knowledge which has been accumulated by the labors of some eighty generations"—that is, during the entire period since the dawn of scientific thought in Europe. In justification of this broad application of the term, he says, "It is so difficult to think of medicine otherwise than as something which is necessarily connected with curative treatment, that we are apt to forget that there must be and is such a thing as a pure science of medicine—a pathology which has no more necessary subservience to practical ends than has zoölogy or botany." In other words, there is a science of disease and an art of healing, both of which are included in the term "medicine," and, as all art is applied science, it is easy to see where the study of the "healing art" should begin.
Pathology is abnormal physiology, or, more broadly, biology, the science of living matter; living matter being recognized by its innate tendency to undergo certain changes of form and to manifest certain physiological phenomena which are universally recognized as constituting organization and life. When these changes of structure or of function become injurious to the organism, or cease to promote its general well-being, they are pathological, but the line of separation is not a distinct one; it is impossible to say with exactness where physiology ends and pathology begins.
It is evident, then, that the science of disease is a branch of the general science of life; and the distinguished lecturer, in making so wide an application of the term "medicine," no doubt intended to assert that the science of biology rests upon the broad foundation of the general physical sciences. The study of medicine, then, consists primarily in the study of biology, including those abnormalities of structure and perturbations of function to which living matter is liable; and, secondarily, medicine deals with the applications of the knowledge thus acquired for the checking of these perturbations and the renewal of normal structures—in other words, for the relief of suffering and the restoration and preservation of health.
The Held of medicine is, then, a large one. As already intimated, some knowledge of the various natural sciences is essential to its successful study; not only by reason of the fact that living matter is subject to the same chemical and physical laws as non-living matter, but also because of the intimacy of its relations to its physical environment, and of the constancy of the reactions between every organism and its environment.
As a general introduction to the course of medical study now opened in this college, it has therefore seemed appropriate to devote an hour to a brief biography of Protoplasm, the universal life-substance from which all organisms, whether vegetable or animal, originate, and modifications of which constitute even the most complex tissues of the highest animal forms.
Though so universally diffused, though the autobiography of protoplasm has been written in the life of every plant and animal since creation's dawn, it is still a hidden story in some of its earlier chapters. Perhaps it is the very simplicity of its origin that balks us: we would fain invoke some supernatural explanation of the growth-force and the capacity for development which belong to this substance, as distinct from non-living matter, forgetting that all natural forces are equally elusive and obscure. Why do certain kinds of matter always crystallize in certain fixed and characteristic forms? Why, on the other hand, is protoplasm formless, but capable of endless development and change?
There are certain chemical and physical differences between crystallizable and non-crystallizable substances which, if fully understood, would no doubt furnish an answer to this question.
Protoplasm, a non-crystallizable substance, is both physically and chemically of a highly complex composition not determined with exactness, but known to consist mainly of hydrogen, oxygen, nitrogen, and carbon, variously combined in such proportions as to produce representatives of three classes of chemical substances—the albuminoids, the starches, and the fats—the albuminous constituents largely predominating in native undifferentiated protoplasm.
With these compounds is associated a considerable though varying proportion of water, as well as smaller quantities of saline and other crystalline substances.
Of the molecular structure of living, active protoplasm, nothing definite is known; it is, however, probable that the albuminoid matter of its massive molecule is associated with a complex fat and with some form of starch; while the water and the salts may be loosely combined either physically mingled or perhaps weakly held together by the feeble chemical affinities which belong to all massive molecules. This constitutes a slime-like mass which, like all chemical compounds, exhibits certain characteristic reactions by which it is clearly distinguishable from certain substances, and known to be closely allied to certain others.
Protoplasm has the power of absorbing water in varying quantities, so that it is sometimes soft and nearly fluid, and again hard and leathery, though ordinarily of a medium consistence and density best described by the term "slime-like" already employed. It is then a glairy, tenacious, semi-fluid substance, transparent, and generally colorless; and if not quite the homogeneous, structureless matter which it was long supposed to be, there is at least an entire absence of differentiation of structure quite comparable to the observed absence of localization of function. When it acts it acts en masse or indifferently, sometimes in one portion, sometimes in another, of its substance, for the production of its simple movements and for the bringing about of its protean forms. Now all mouth, and anon all stomach, at times all feet, and again all lungs, it fulfills Dryden's famous description, "Everything by starts, and nothing long," save that it is ever and always protoplasm.
Like other albuminous substances, it is coagulable by heat, by alcohol, and by mineral acids, and is similarly stained by iodine and by nitric acid. Living protoplasm possesses also certain fundamental properties by which it may be distinguished from dead protoplasm. Prominent among these properties, grouped under the single term "vital," may be mentioned first, excitability, or, as it is more commonly called, "irritability" by which is meant the power of responding to a stimulus. An amoeba suddenly brought in contact with some foreign body responds to the stimulus so received by certain characteristic movements.
The movements of protoplasm, however, can not always be thus traced to some external exciting cause. Watching a specimen beneath the microscope, portions of the mass may be seen to creep, or rather to flow, slowly away in fine threads uniting with other threads from different parts of the same mass, thus forming an irregular net-work. Or perhaps it thrusts out temporary feet indifferently from any part of its surface by means of which it creeps slowly about, and it draws them in again, returning to the somewhat globular shape which appears to belong to its quiescent state. These movements are spontaneous; that is, they originate in the mass and result from the essential constitution of this kind of matter; therefore protoplasm is described as "automatic" or self-acting, and even as having a will of its own.
The internal changes which bring about these movements are believed to be identical with those which occur in muscle-tissue under stimulation, producing the change of form in muscle-fiber known as contraction; hence protoplasm may be said to be "contractile" and this is another of its so-called vital properties.
Protoplasm also feeds upon nutritive material brought into contact with its surface. This it does by flowing around the substance, whatever it may be, which serves for its food, thus inclosing it in a temporary stomach improvised anew for each occasion, and becoming gradually obliterated as the new material slowly dissolves and is absorbed, mingling and chemically combining with the already existing protoplasm, and thenceforth forming a part of its substance. In other words, certain kinds of dead matter called food are assimilated, converted into living protoplasm by those processes of absorption and chemical union which constitute nutrition in all living things. Hence, protoplasm is "assimilative" and this is another of its vital properties. Side by side with this process of taking in new material and converting it into its own substance, there is also another process going on—that of rejection of old, broken-down, effete matter which has not only become useless to the living protoplasm, but would be injurious if retained.
The life of protoplasm is thus seen to consist in a double series of chemical changes, by one of which its substance is constantly renewed and built up; by the other, it as constantly breaks down, the products of decomposition being gradually rejected from the living, ever-fluctuating mass, which thus becomes the theatre, the arena, of life.
What is the outcome of this constant play of chemical and physical forces—this incessant interchange of matter between the mass of protoplasm and its environment? In other words, what is the meaning of the life thus manifested? Its significance is this: The production and manifestation of new and higher kinds of force than any belonging to inanimate, inorganic matter.
In the life of protoplasm we behold the dawning of voluntary motion—of those spontaneous movements especially characteristic of animals (though shown to a slight extent by plants as well), and exhibited in the highest degree by man in the thousand muscular adaptations displayed in his complex mechanism.
But the doctrine of the correlation of forces formulates the fact that the amount of force in the universe of matter is constant and unvarying; that, as matter is indestructible, so the forces which it manifests are persistent—never increasing, never diminishing. Whence, then, comes this new and higher kind of force called spontaneous motion? It is a law of physics that, as elemental molecules aggregate to form those which are more complex and massive, the force previously manifested by the simpler molecules becomes potential or latent, as it was formerly expressed; and that in the breaking down of these more complex molecules, in their return to their former simple state, this hidden force springs into activity again, not necessarily reappearing, however, as the same kind of force; there is not only a storing up of energy, but a transformation, a remolding of it in other and, in the case under consideration, higher kinds. As the wide and rapid vibrations which constitute the expansive power of steam are made, by means of suitable mechanical appliances, to disappear in condensation and to reappear as locomotion, so the potential forces locked up in the molecules of protoplasm appear in the breaking down, the decomposition, of these molecules as spontaneous movements of some portions of the mass.
The energy expended in the movements of protoplasm is supplied through the chemical changes going on in its substance, by the breaking down of compounds possessing much latent energy into more simple ones containing less such energy.
These downward chemical changes are mainly processes of oxidation, one of the chief products of oxidation being carbonic-acid gas. Now, the taking in of oxygen and the giving out of carbonic acid together constitute respiration; hence protoplasm is "respiratory"—another of its vital properties. It breathes, as the fish does, by absorption of oxygen from its surrounding medium; but it breathes at the entire surface of its mass instead of at special parts of its surface, as in the fish. This is true of vegetable as well as animal protoplasm, the two being indeed regarded, in all essential points, as identical.
Protoplasm is also "reproductive." Haeckel, in his history of the discovery of the monera, which consist of little globules of simple protoplasm, describes their mode of reproduction as follows: "The little creature divides into two halves, and each of these goes on living like the original one."
But there is a form of living protoplasm even more simple, if possible, than the moneron of Professor Haeckel—the Myxomycetæ—of which a very good description may be found in the inaugural address of Professor Allman, President of the British Association, in 1879, published in the October number of "The Popular Science Monthly" of that year. These organisms consist, during the greater part of their lives, of simple protoplasm. They may be found in moist places growing on decaying leaves, rotten wood, etc., etc., over which they spread in the form of a net-work, exhibiting amœboid movements, appearing to be sensitive to the light, and giving other evidences of life.
But we may find a specimen of protoplasm even nearer home than this. Prick your own fingers, if you choose; withdraw a drop of living blood from the wound, and, having properly diluted it, place it under your own microscope for observation. Scattered among the numerous small bodies which give to the blood its brilliant crimson hue, may be seen a few somewhat larger colorless ones—the leucocytes or white cells.
These microscopic bodies consist mainly of simple, undifferentiated protoplasm. They* differ from the monera (first found by Haeckel floating on the surface of the Mediterranean Sea) in being nucleated; that is, they contain a central kernel, the nucleus, which is more dense than the surrounding protoplasm, and of a slightly different chemical composition. These bodies, which circulate among the tissues with the blood forming a part of it, manifest independent movements, thrusting out and drawing in portions of their mass in true amœboid fashion; they devour solid particles of matter which come in their way—their smaller comrades, the red corpuscles, not always escaping their voracity. This they do by flowing around and inclosing them, as already described. They have also been observed by Klein to multiply by division, like the monera. The white blood-corpuscle, identical, apparently, with the amœba, which may be found in the standing water of pools attached to the surface of leaves, and in many other similar situations, is a true cell—the morphological unit from which all organisms, whether low or high, originate, and by whose multiplication, development, and differentiation, all the tissues of their bodies are produced.
The history of the growth and development of every animal—whether moner, mollusk, or man—is a history of cell-multiplication and cell-differentiation; and the most highly endowed individual of them all possesses no property, no faculty, no power, which is not at last foreshadowed in the formless, structureless, protoplasmic cell from which they are all alike derived. Is the nervous tissue of man in the highest degree irritable and automatic—that is, sensitive and self-acting? So is protoplasm, though in an almost infinitely less degree. Is muscular tissue eminently contractile, serving for the production of the varied and complicated movements of all parts of the body? Protoplasm is also capable of slight spontaneous motions of its entire mass. Are the various glands of the body actively secretory and excretory? So is protoplasm within the narrow limits of its chemical necessities. Equally, also, with the highest tissues and organisms, it reproduces its kind.
The complex body of any one of the higher animals may, then, be considered as consisting of certain tissues, each of which has not only been derived from protoplasm but each of which corresponds, in its perfected function, to some one of the fundamental properties of protoplasm, to the special manifestation of which it is devoted for the benefit of the organism as a whole, on the important principle first spoken of by Milne-Edwards as the physiological division of labor. Division of labor among the tissues, however, as among the members of a community, has its limits. While every tissue has some leading quality, some special function, developed to the highest degree in the interests of the organism as a whole (contraction in muscle-tissue, secretion in gland-tissue, and so on), yet each tissue retains in its own private interests, as it were, vestiges of all the other protoplasmic properties belonging to their common ancestor. Hence, all the tissues are assimilative to the extent of keeping up their own nutrition; all are to some degree irritable, all are capable of reproduction of their own kind of cells, and so on.
Thus, from the beginning of his career, as a microscopic speck of living matter, to its close, although he figures as the most highly endowed and transcendent of beings, man, biologically considered, is protoplasm, protoplasm, only protoplasm; and, whatever his perfections, regarded as a member of the animal series, he has the high privilege of knowing if not of feeling himself the brother of all living things. With Job, he may say unto the worm, "Thou art my mother and my sister." "Oh, why should the spirit of mortal be proud?"
"What, then, is protoplasm?" we are inclined to ask, almost at the close of our attempt at a description.
Professor Huxley has called it "the physical basis of life"—an expression which has become classic in the scientific world—while life, in its turn, is defined as a property, or congeries of properties, of protoplasm. Pflüger has naively said, "Albumen lives" that is, becomes protoplasm—"when it begins to take in oxygen"; and Foster, with equal simplicity, remarks, "The whole secret of life may almost be said to be wrapped up in the occult properties of certain nitrogen compounds."
Lewes, in his own graphic style, has said, "The organism and its environment are the two factors, of which life is the product."
Protoplasm is the agent by which the energy of non-living matter is converted into that of living matter—the sacred fire which is never permitted to go out, but perpetually glows on the altar of Nature, fed by the vestal forces of the environment, and burning ever higher and higher through those twin influences, heredity and the survival of the fittest.
This true "vital spark" is not only transmitted from generation to generation in the entire animal world, each reproducing its own kind, but it has been handed on, through vast geological ages, from branch to branch of the animal tree, since that far-off period when the "dawn animal" first left its imprint in the hardening mud of its slimy bed at the bottom of a vast ocean whose waters were still under the influence of the earth's heated interior, when this ocean was overhung by a sky dark with clouds so dense that day and night were scarcely distinguishable, and shutting in an atmosphere heavy with carbonic-acid gas.
The relations observed between the fossil animals thus far discovered, the existing animal series, and the embryonic forms of all animals at the various stages of development of their respective embryos, are most significant. The earliest, oldest known fossil (the Eozoön Canadense, or "dawn-animal," the genuineness of which, though denied by some, is more than probable) belongs to the same class of organisms as the moneron and the amœba of to-day, which stand at the bottom of the scale of animal life; and the geological ladder in its ascent bears upon its successive rounds fossils which correspond, with more or less exactness, to the ascending series of now living forms; showing, however, in addition to these, many connecting links between existing classes, which, in the progress of time and development, have diverged widely from each other; while the modern science of embryology as clearly shows that the development of the human being—beginning in a formless, structureless, microscopic speck of protoplasm, comparable in all appreciable respects to the "dawn-animal" of the Palæozoic period, and to the moneron and amœba of to-day—consists in the ascent, step by step, with a good degree of exactness, both of the geological ladder and of the trunk of the animal tree whose branches represent all existing forms of animal life, whose roots are deeply imbedded in the inorganic crust of the earth, and at whose apex appears the genus homo—the crown and consummate flower of organic development. In other words, the individual development of every human embryon is a brief résumé (in which, it is true, some of the chapters are suppressed and others greatly condensed) of the history of the development of animal life on the globe, from its infancy to the present day.
In 1862 Professor Graham pointed out the importance of the two states of matter, described by him as crystalloid and colloid—crystal-like and jelly-like. He says: "The colloidal state is, in fact, a dynamical state of matter; the colloid possesses energy, and may be regarded as the primary source of the forces appearing in the phenomena of vitality."
Although certain colloids have a very simple chemical composition (as silica, for example, which, ordinarily crystalloid, is capable of existing in a colloidal state), the molecular constitution of the colloids in general is undoubtedly highly complex. The molecule of albumen (a typical colloid closely resembling protoplasm), while it consists of but six different chemical elements, is estimated as containing several hundred atoms of these elements, which thus render the molecule an extremely massive one.
Now this massiveness of its molecules confers upon protoplasm a certain mechanical stability favorable to the preservation of organic forms; at the same time endowing it with the chemical instability essential for the constant exchanges of material which constitute nutrition and are characteristic of all living matter.
These massive molecules are also reservoirs of vast amounts of energy of the kind long known as potential—a term which, though likely to vanish, not into thin air but into the thinner ether, is nevertheless a very convenient one. This potential energy, stored up during the slow processes of plant-life and appropriated by animals in the form of food, is liberated or manifested as actual energy in the decomposition of their tissues that is, in the gradual breaking down of tissue-cells, by means of which the animal functions are performed, and carbonic acid, urea, and other excretory compounds are produced.
But a large part of the tissues which make up the bodies of adult animals have, in a great measure, lost their resemblance to the protoplasm from which they were derived, through an extreme development which has resulted in tissues quite unlike each other—some of them, as the bones, for example, evidently serving a purely mechanical purpose in the body; and it may be said that a comparatively small proportion of the tissues of the body are, strictly speaking, living. Professor Beale classifies all the material of the tissues, and even of the ultimate cells from which the tissues are derived, under two heads, as formative and formed—that is, matter which has the power of producing new matter like itself out of pabulum or food, and that which has no such power, but which has been produced by the former. He considers that a muscle-fiber is not, like the protoplasm which produced it, living; and that the nerve-fiber also consists of formed material of which protoplasm is the builder.
In accordance with this view, only the lowest—that is, the nutritive—processes can be regarded as truly vital. The higher functions performed by the perfected tissues—the bones, the muscles, and the entire system of nerve-fibers and nerve-centers, including the brain are mechanical rather than vital; the character of the function in each case depending on the character of the mechanism, i. e., on the particular relations of the parts concerned.
Muscle-tissue, for example, has but a single and simple physiological property, the power of change of form called contraction, and even this is a function of formed material rather than of living matter; but, through the mechanical relations of bones and tendons, of joints and ligaments, of associated and opposing individual muscular bundles, all the complicated and varied movements of the body are brought about.
The action of muscle is one and the same, whether it be expended in the grosser movements of locomotion, in the finer manipulations of the skilled artisan and the musician, or in the still more delicate adjustments of the vocal cords, by means of which the exquisite modulations, almost infinite in variety, of the voice of a Patti or a Campanini are produced.
These various adjustments are evidently mechanical in their nature. The so-called vital processes—processes identical with those taking place in the simplest animal that lives, and in the very grass beneath our feet, perform a comparatively humble part in the production of the vast results. The vital processes are concerned in the building up of the tissues and organs produced by and from protoplasm out of the food supplied to it; and the chemical changes involved in the breaking down of the tissues furnish the initial force in each case; but the actual forces manifested are due to transformations of this initial force brought about by the complicated mechanism which this force serves to set in operation.
The powers and possibilities of protoplasm may be crudely compared to those of steam, the expansive property of which may be observed in a simple apparatus for the grinding of coffee, for example, or in the operations of a magnificent Corliss engine, by which all the complicated machinery of an entire Exposition may be set in motion. The steam has precisely the same properties in the two cases, but the resulting forces differ in proportion to the complexity and multiplicity of the relations of the parts of which the different mechanisms are respectively composed.
In the study of the highly complex mechanism, the human body—which constitutes the study of medicine—all the powers and properties of matter must be duly considered and taken into account, for all are concerned in the production of its forces and in the performance of its functions; not one is violated or turned out of its natural course, but all combine in a harmony more complete than is manifested by any other known combination of materials and forces. Heterogeneousness the most extreme, complexity the most intricate, actions and reactions the most delicately balanced, all unite, in the play of the forces of the body, in the production and manifestation of its varied powers.
The study of science in any of its numerous departments is intrinsically elevating and ennobling if it be pursued in the true scientific spirit, viz., in the desire and search for truth for truth's own sake; and, while the pursuit of medicine has its practical side in preparing its votaries for the service of suffering and sick humanity—perchance for making the blind to see, the deaf to hear, and the lame to walk—it also broadens and enriches their own individual characters and lives, since it leads them into the green pastures by the still waters of the eternal truths of nature, at the same time bringing them into the still higher experiences of sympathy and charity toward all mankind.
- ↑ Address delivered at the opening of the Thirty-second Annual Session of the Woman's Medical College of Pennsylvania.