Plasma (biology)

“ Plas′mic, pertaining to plasma, protoplasmic.—ns. Plasmō′dium, composite masses of primitive protozoa, in which numerous units are fused, or in rare cases simply combined in close contact; Plas′mogen, true protoplasm; Plasmog′ony, the generation of an organism from plasma ”

“ The study of the permeability to various substances of what we may perhaps consider as the most simply organized cells in the whole body, the colored corpuscles of the blood, promises to throw a flood of light on absorption in general. It has been lately shown that they are practically non-conductors of electricity in comparison with the liquid portion of the blood, or plasma, in which they float. This is due to the fact that the salts of the plasma, whose ions carry the electricity, penetrate the corpuscles with difficulty, sodium chloride, for example, scarcely passing into them at all. ”

“ In other words, in so far as it has been studied in this respect, cell plasma exhibits exactly the same responses to variations in the proportions of salts (electrolytes) in solution, that artificial emulsions of oils (fats) in water do; and the normal, or critical, equilibrium proportion of these electrolytes for all colloidal complexes is that in which they occur in sea-water. It must be admitted that there is as yet no definite evidence that the observations which have been made upon the protoplasm of animal tissues will apply equally well to plant cell protoplasm. ”

“ Blood Plasma.—The plasma is a solution in water of a varied number of substances, and as a solvent it confers on the blood its power of acting as a carrier of food stuffs and waste products. One important food substance, oxygen, is, however, only partly carried in solution, being mainly combined with haemoglobin in the red corpuscles. ”

“ The elements of our tissues have their nutrition kept up by a constant movement of supply and withdrawal, new molecules replace the old ones, and acts of assimilation and disassimilation find by turns in the plasma their point of origin and completion. The blood-globule is nourished just as the constituent parts of the glands, the muscles, the nerves, and the brain are, and the only difference to be noted in this respect is that the process takes place within the very plasma itself, while the other elements are parted from it by the thin membrane of the capillary vessels. ”

“ There can be no doubt that the plasma is the chief seat of differentiation, as Minot has emphasized, and that highly differentiated cells, such as muscle, nerve, and some kinds of connective tissue, have a larger amount of plasma and its products, relative to the nucleus, than have embryonic cells. In the case of fiber cells, fat cells and probably muscle cells, the cell body becomes filled with the products of differentiation and metabolism, which like the yolk in egg cells, or the secretion products in liver cells can not enter the nucleus and consequently do not influence its size. ”

“ By introducing substances which are out of harmony with the species, and more particularly with the plasma, we bring into the organism bodies which are, in their whole structure, absolutely disharmonious with the cells of the body. ”

“ The food stuffs carried by the plasma are proteins, carbohydrates, salts and water. The main waste products dissolved in it are ammonium carbonate, urea, urates, xanthin bases, creatin and small amounts of other nitrogenous bodies, carbonic acid as carbonates, other carbon compounds such as cholesterin, lecithin and a number of other substances. Thus, if we take mammalian blood as a type, the plasma would have the following approximate composition:—
Proteins.—The proteins of the blood plasma belong to the two classes of the albumins and the globulins. ”

“ For we may here at any moment, by means of the microscope, point out the wonderful fact, first established by Dujardin and Max Schulze, that the formless mucus of the soft plasma-body, this true “matter of life,” is able to secrete the neatest, most regular, and most complicated structures. This secretive skill is simply a result of inherited adaptation, and by it we learn to understand how this same “primæval slime”—this same protoplasm—can produce in the bodies of animals and plants the most different and most complicated cellular forms. ”

“ The existence of this diffusion-preventing or insulating surface-film, the plasma-membrane, is thus a necessary condition of the stability of the living system and hence of the continuance of the life-processes. The living condition is in fact incompatible with marked and permanent increase in surface-permeability. During life the semi-permeable condition is retained; on death there is always a marked increase in the permeability of the plasma-membrane; the cell then undergoes a ready and rapid dissolution or cytolysis, and the constituents serve as food to bacteria. ”

“ The blood-globule not only lives its individual life within the plasma, but it needs, in order to complete its function of vivifying every part of the body, to absorb oxygen from the air, and it then takes that bright vermilion color which is characteristic. ”

“ Further, the cause of disharmony with the blood plasma may depend upon the fact that cells of a particular kind have degenerated, in consequence of which they have a pathological structure, and give off a disharmonious kind of material, to which the blood plasma is unused. ”

“ All this would lead to numerous possibilities, which would exclude all regularity in the metabolism of the cells, as well as in the general metabolism of the body.
The animal organism prevents all these possibilities by allowing only material which has been put in harmony with the body, and particularly the plasma, to reach the circulation. The nutritive material of the tissue cells, which from this point of view can be considered homogeneous, gives decomposition stages with which the cells have been long familiar. Nothing that is disharmonious appears on the scene. ”

“ It may be assumed that a transparent tissue composed of cells can only maintain its translucency so long as the most perfect equilibrium is maintained as regards the mutual relation of the cells, the pressure of its interstitial plasma, and the chemical composition of both plasma and cell structures. ”

“ Only serum and plasma which are absolutely free from hæmoglobin must be used for these experiments. To a measured quantity of serum or plasma a certain quantity, in cubic centimetres, of an albumen, peptone, or polypeptide solution, having a known composition in regard to substrates, is added; a polariscope tube is filled with the mixture, and the rotation is quickly ascertained by means of a good polariscope. The tube is then placed in an incubator, and from time to time the angle of rotation is again noted. ”

“ Thus we see a living plasma is not necessary for the blood corpuscles: they flourish in a dead one. The blood plasma is not alive.
In the days of venesection we were taught that the last act of vitality in blood when drawn from the body was its coagulation, but is this really any more a vital process than the clotting of sour milk? I think not.
In the same category with milk and blood plasma, we must place lymph, the fluids in the pleura, pericardium, peritoneum and synovial sacs, and also the cerebro-spinal fluid; none of them is alive. ”

“ In every case where we have with great difficulty succeeded in examining the plasm as far as possible and separating it from the plasma-products, it has the appearance of a colorless, viscous substance, the chief physical property of which is its peculiar thickness and consistency. The physicist distinguishes three conditions of inorganic matter—solid, fluid, and gaseous. Active living protoplasm cannot strictly be described as either fluid or solid in the physical sense. ”

“ The external form is quite irregular, continually changing, globularly contracted when at rest. Our sharpest discrimination can detect no trace of an internal structure, or of a formation from dissimilar parts. As the homogeneous, albuminous mass of the body of the moner does not even exhibit a differentiation into an inner nucleus and an outer plasma, and as, moreover, the whole body consists of a homogeneous plasma or protoplasma, the organic matter here does not even reach the importance of the simplest cell. ”

“ We have seen how little mere form has to do with the essential properties of protoplasm. This may shape itself into cells, and the cells may combine into organs in ever-increasing complexity, and protoplasm-force may be thus intensified, and, by the mechanism of organization, turned to the best possible account; but we must still go back to protoplasm as a naked, formless plasma if we would find—freed from all non-essential complications—the agent to which has been assigned the duty of building up structure and of transforming the energy of lifeless matter into that of living. ”

“ For an Amœba is nothing but a simple primary cell, a naked little lump of cell-matter, or plasma, containing a kernel. The contractility of this plasma, which the free Amœba shows in stretching out and drawing in its changing processes, is a general vital property of the organic plasma of all animal as well as of all vegetable plastids. When a freely moving Amœba, which perpetually changes its form, passes into a state of rest, it draws itself together into the form of a globule, and surrounds itself with a secreted membrane. ”

“ Carbon atoms begin their organism-engendering activity, and unite with the other elements into plasma-combinations capable of growing. One small plasma-group oversteps the limits of cohesion and individual growth; it falls asunder into two similar halves. With this first moneron begins organic life and its most distinctive function, heredity. In the homogeneous plasma of the monera, a firmer central nucleus is separated from a softer outer mass; through this differentiation of nucleus and protoplasm arises the first organic cell. ”

“ Substances, which may be indifferent products for one kind of cell, may be injurious to another kind. Each cell produces secretions of its own, in the formation of which many intermediate stages are passed through. If the whole transformation into substances that will be in harmony with the plasma be performed inside the cell, then any by-products that may appear, even though they be not indifferent in regard to other cells, will display no injurious activity in the organism as a whole. ”

“ This is caused, according to the view of Franz Hofmeister and others, by the formation of ferments or enzyma—in other words, by catalysators of a colloidal structure. Verworn has, on physiological grounds, given the name of biogens to these plasma-molecules.
The profound insight which comparative anatomy has given us into the significance and nature of organs, and comparative histology into those of the cells, has naturally excited a desire to penetrate in the same way the mystery of the elementary structure of the plasm, the chief active constituent of the cell. ”

“ The fact that the animal organism replies to the invasion of disharmonious substances—which, either taking their origin from the metabolism of certain cells of its organs, or being normal constituents of the cells, pass directly into the blood plasma—by means of specifically directed ferments, is of the greatest importance to physiology as well as to pathology. ”

“ But when plasma of normal animals was mixed with albuminous bodies and placed in a dialysation tube, no substances giving the biuret reactions could be traced in the outer fluid, even after standing for many days. Finally, it has been proved quite recently that, by mixing the plasma or serum of specially treated animals with albumen, the nitrogenous contents of the outer fluid increase to a considerably greater extent than when the plasma of normal animals and albumen are mixed together. ”

“ The possibility of breeding single cells and pieces of tissues in the blood plasma outside the organism, and keep them alive for a certain time, opens out a prospect of answering many problems by experimental means. We shall see in due course why some of the cells lose their normal functions when the secretion of certain organs is lacking. The number of possibilities is almost unlimited. For example, some substances, such as grape sugar, can only be dissociated by the cells into final products—carbon dioxide and water—after they have been prepared in a certain manner. ”

“ This supplies heat and the other forms of bodily energy. Entering as a free element, oxygen leaves the body as a part of the waste compounds which it helps to form. The free oxygen is transported from the lungs to the cells by means of the hemoglobin of the red corpuscles, while the combined oxygen in carbon dioxide and other compounds from the cells is carried mainly by the plasma. The limited supply of free oxygen in the body at any time makes necessary its continuous introduction into the body. ”

“ What is this mysterious "living substance" that we find everywhere as the material foundation of the "wonders of life"? Plasm, or protoplasm, is, as Huxley rightly said thirty years ago, "the physical basis of organic life"; to speak more precisely, it is a chemical compound of carbon that alone accomplishes the various processes of life. In its simplest form the living cell is merely a soft globule of plasm, containing a firmer nucleus. ”

“ Before dealing with the case of the living plasma-membrane, it will be necessary briefly to describe some of the methods by which artificial membranes, similar in many of their osmotic and other physical properties to plasma-membranes, may be prepared, and to consider some of the properties of these membranes. The tendency of the living cell (or living system) to surround itself with a membrane will then be seen to be in no sense a distinctively vital peculiarity, but one which it exhibits in common with a great many non-living systems. ”