Membrane

“ 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. ”

“ Every serous membrane is moistened on its internal surface by a fluid almost the same as the serum of the blood. The exhaling orifices constantly pour it out and it is constantly taken up by the absorbents. ”

“ Those, which open their innumerable mouths into the cells of the whole cellular membrane; and whose use is to take up the fluid, which is poured into those cells, after it has done its office there; may be called cellular absorbents.
Those, which arise from the internal surfaces of the membranes, which line the larger cavities of the body, as the thorax, abdomen, scrotum, pericardium, take up the mucus poured into those cavities ”

“ In many instances this membrane is formed of very thin flattened cells, in other instances it is apparently a homogeneous membrane, and according to some observers is simply a modified part of the basal surface of the cell, while according to others it is a definite structure distinct from the epithelium.
In the secretory portion of the gland and in the smaller ducts the epithelial layer is one cell thick only. In the larger ducts there are two layers of cells, but even here the surface cell usually extends by a thinned-out stalk down to the basement membrane. ”

“ On its surface is formed a perfect membrane, which is everywhere free on its outer face. There are two processes in the formation of a cell; the first is the isolation or individualising of a part of the contents of the mother-cell, the second the formation of a membrane round the individualised portion.' He then proceeds to show that the cell-wall is formed by the separation of non-nitrogenous molecules from the nitrogenous mucilage (proto-plasm) . These sentences contain all that is general and essential in vegetative cell-formation. ”

“ When a membrane separates two fluids, holding in solution different ingredients, the fluids pass through the membrane in an imperceptible manner, and mix or exchange their elements. The force which produces these effects is capable of balancing a very considerable pressure. It appears, moreover, to depend, at least among other causes, upon attractions operating between the elements of the solids and the fluids, as well as between the different fluids; and this force, though thus apparently of a mechanical and chemical nature, probably has considerable influence in vital phenomena. ”

“ There are two germinal membranes, respectively representing the Instrumental and Alimental Systems. Each membrane differentiates, by different appropriations of the yolk substance, into three primary layers, epithelial, neural, and muscular. In the epiblast, or upper membrane, these layers represent: 1°, the future epidermis with its derivatives—hair, feathers, nails, skin glands, and chromatophores; 2°, the future nervous tissue; 3°, the future muscular tissue.130 (Bone, dermis, connective tissue, and blood-corpuscles are subsequent formations.) ”

“ But there is another kind of diffusion—osmose, or membrane diffusion. When liquids of different densities are separated by a thin membrane, diffusion takes place through this partition with a rapidity depending on the nature of the liquids and membrane, the greater flow being toward the denser fluid. The cell-wall of a root-hair is such a membrane, separating the denser liquid within the cell from the thinner one without; and, as this membrane is a living, growing one, it may be specially effective for osmotic action. ”

“ The inner membrane, when viewed under a high power, is seen to be covered with the minutest spines; the external membrane is structureless, except that there are a few rows of very minute beads of hard chitine, like those which occur on the capitulum of Conchoderma aurita. Lovén, however, states that there are imbedded in the outer membrane, scattered, minute, dendritic, calcareous particles. Of these, I could see no trace. There is a very thin muscular layer between the two coats, all round the capitulum, and this layer becomes rather thicker round the base, near the peduncle. ”

“ But some cells, especially young ones, are entirely without the enveloping membrane, or stiff wall. Hence we now generally describe the cell as a living, viscous particle of protoplasm, enclosing a firmer nucleus in its albuminoid body. There may be an enclosing membrane, as there actually is in the case of most of the plants; but it may be wholly lacking, as is the case with most of the animals. There is no membrane at all in the first stage. The young cells are usually round, but they vary much in shape later on. ”

“ These membranes are present in all living cells without exception, whether a visible external layer is present or not. Thus red blood corpuscles, though typically naked cells, show by their behavior in salt-solutions of varying concentration that they are bounded by a difficultly permeable surface-layer which is different in its physical properties from the internal protoplasm—having in fact the essential properties of a semi-permeable membrane. ”

“ You know that if substances of a certain kind are placed in solution next to each other and separated only by a thin porous membrane, there will take place and interchange of the molecules or ions of the one substance with those of the other until the two liquids are completely mixed. ”

“ More convincing than these are membraneous pieces, which may be obtained of various sizes. (See figs. 5, 6.) I have a drawing of such a fragment, which, if enlarged as figs. 1 and 2, would cover over one-quarter of the page, and to which a number of nuclei, more than six, are attached. As a rule, this membrane will, by the manipulations with the cover-glass, not be spread out, but rather folded up, huddled together inclosing some of the gland cells, forming an indescribable nest. ”

“ There are membranes in all sanguineous animals. Membrane is like a dense thin skin, but it differs in kind, for it is neither divisible nor extensible. There is a membrane round every bone and every intestine, both in the greater and smaller animals; they are inconspicuous in small animals, owing to their thinness and small size. The principal membranes are two, which surround the brain, one round the bones of the head, and this is stronger and thicker than that round the brain itself; and after these, the membrane which surrounds the heart. ”

“ The fact of the conveyance of fluids and other matters along the ciliated surface, as well as the direction in which they are impelled, may also be made manifest by immersing the membrane in fluid, and dropping on it some finely-pulverized substance (such as charcoal in fine powder) , which will be slowly but steadily carried along in a constant and determinate direction. ”

“ The membrane or velum is thin, and is really a great expansion of a dorsal membrane similar to that which is found along the median dorsal line of the two posterior arms. The suckers of the originally posterior series of each dorsal arm lie along the external border of the shell, and the arm with its two rows of suckers extends round the whole border of the membrane, the arm being curved into a complete loop, so that its extremity reaches almost to the origin of the membrane near the base of the arm, the extremity being continued on to the internal surface of the membrane. ”

“ The external membrane of the body is turned inwards at the orifice, as a short flattened tube, which widens considerably (being, in a middle-sized specimen of Coronula, 4/100ths of an inch in width) before it abruptly terminates. The meatus, as I have called the sack-like cavity which encloses the true acoustic sack or vesicle, is formed of pulpy membrane, and is apparently continuous with the corium of the whole body, but by dissection it can be separated entire. The acoustic vesicle is of various shapes, as we shall immediately see ”

“ It is curious to notice how our body is wrapped in membrane. On the outside, is the skin protecting from exterior injury, and, on the inside, is the mucous membrane reaching from the lips to the innermost air cell of the lungs. Every organ is enveloped in its membrane. Every bone has its sheath. Every socket is lined. Even the separate fibers of muscles have their covering tissue. The brain and the spinal cord are triply wrapped, while the eye is only a membranous globe filled with fluid. ”

“ Hence, after a time, the membrane will not be sufficiently nourished by the membranogenous substance, it will break down, and an aperture will occur through which the interior liquid oozes out, forming in its turn a new {125}membranous covering for itself. This is the explanation of the fact that all living organisms are formed by colonies of microscopical elements, although we must not forget that Nature often produces similar results in different ways. ”

“ The protoplasm of the cell is usually large in amount and often contains large numbers of granules.
The individual cells forming an epithelial membrane are classified according to their shape. Thus we find flattened, or squamous, cubical, columnar, irregular, ciliated or flagellated cells. Many of the membranes formed by Varieties. these cells are only one cell thick, as for instance is the case for the major part of the alimentary canal. In other instances the epithelial membrane may consist of a number of layers of cells, as in the case of the epidermis of the skin. ”

“ These membranes which comprehend, as has been said, the periosteum, the dura-mater, the sclerotica, the albuginea, the peculiar membrane of the spleen, the kidneys, the corpus cavernosum, &c. are almost all destined to form external coverings, kind of sacs in which are contained the organs they invest. ”

“ What is the nature of this common membrane? I am entirely ignorant; though with a different appearance it has the greatest analogy with the preceding coat, in its properties. We cannot class them in any system. They form a separate texture in the economy, a texture that has properties entirely distinct.
When we dry the common membrane of the arteries by itself, it is infinitely more pliable than the other. It remains transparent, the other does not. As to the phenomena of the other re-agents, except the horny hardening, they are nearly the same. ”

“ Of the two sides of the heart, the membrane which lines the left is unquestionably the more liable to disease. But my own observation would never have led me to conclude that the membrane of the right side was so far exempt as it is commonly thought to be. Speaking from the best recollection I have of the specimens which have fallen under my examination, I should say that, in one-third of the cases where disease has been found on the left side, it has existed on the right side also, and been essentially of the same character. ”

“ When it is dried in considerable layers, its cells adhere together, and these layers being stretched a little to facilitate the drying, represent a true serous membrane, so that it would be impossible to distinguish it from one dried in the same way. ”

“ Another method of increasing absorption from the cellular membrane is by warm air, or by warm steam. If the swelled legs of a dropsical patient are inclosed in a box, the air of which is made warm by a lamp or two, copious sweats are soon produced by the increased action of the capillary glands, which are seen to stand on the skin, as it cannot readily exhale in so small a quantity of air, which is only changed so fast as may be necessary to permit the lamps to burn. ”

“ The skin and central nervous system are developed in the External, or upper membrane; the osseous, muscular, vascular, reproductive, and urinary systems, the walls of the alimentary canal, and its appendages, are produced in the Middle membrane; while the epithelium, which lines the alimentary canal and its appendages, the lungs, liver, etc., is derived from the Internal or lower membrane. ”

“ In the egg of the silkworm the outer membrane is comprised of an inner reticulated membrane of non-nucleated cells, in the outer layer the cells are arranged in an irregular circular form, also non-nucleated, with minute interstitial setæ or hairs projecting outward. ”

“ A germ which has undergone no developmental modifications, consists of a spheroidal group of homogeneous cells. Universally, the first step in its evolution is the establishment of a difference between some of the peripheral cells and the cells which form the interior—some of the peripheral cells, after repeated spontaneous fissions, coalesce into a membrane; and by continuance of the process this membrane spreads until it speedily invests the entire mass, as in mammals, or, as in birds, stops short of that for some time. ”

“ Small pointed [Pg 30] spines, connected with the underlying corium by tubuli, are not unfrequently articulated on this membrane: the tubuli, however, are often present where there are no spines. To allow of the growth of the capitulum, the membrane between the valves splits at each period of exuviation, when a new strip of membrane is formed beneath, connected on each side with a fresh layer of shell,—the old and outer slips of membrane disintegrating and disappearing: when there are many valves, the line of splitting is singularly complicated. ”

“ Those who enumerate three tunics are, I believe, in error, owing to the ancients having described the same membrane at one time under the title of “chorion,” from the concourse of veins, at another under the name of “allantois” from its form.
Unquestionably, every “conception” is inclosed in two envelopes, just as the brain is surrounded by its two membranes; every tree and fruit, moreover, has its double bark; and lastly, seeds and fruits are protected by a double covering, the outermost of which is harder and stronger than the inner one. ”