Osmosis

“ Osmosis, in van Laar's theory depends not upon the molecules of the dissolved substance, but upon the solvent itself, which, having the higher chemical potential, moves toward the solute. To explain the phenomena of osmosis by appealing to an initial osmotic pressure, says van Laar, [41] is like saying that an angry man's loud talk and unseemly gestures are due to his red face. [42] Anger is the real cause of both. So the movement in osmosis, which produces a difference in hydrostatic pressure, depends initially upon differences of chemical and thermodynamic potentials. ”

“ Physiological Importance of Osmosis.—It is not an exaggeration to say that osmosis is a process not only of great importance to a plant, but to an animal as well. Foods are digested in the food tube of an animal; that is, they are changed into a soluble form so that they may pass through the walls of the food tube and become part of the blood. ”

“ The yeast-cell grows, pushes forth bud after bud, liberates particle after particle of carbon dioxide, all under increasing pressure the further the process goes, until at last at the supreme moment oak and iron can endure no more—the barrel bursts! Here no one can quote osmosis, although as between the contents of the cell and the surrounding liquid osmosis doubtless there is, as there was in the case of the maple; but osmosis is certainly not responsible for the gas-pressure under which the cells are working. ”

“ Osmosis takes place when two fluids of different osmotic pressure are separated by animal membrane. Difference in osmotic pressure is due to differences in molecular concentration, the greater the number of molecules the greater is the pressure, and the greater rapidity of flow is from the fluid of less pressure to the fluid of greater pressure. The molecular concentration of tissue and blood fluid is constantly being equalized by the process of osmosis. ”

“ We have then by exposing the fish to water put water back in the cells and taken out the excess salt. The actual food material of the fish–the cell protein–is still where it was, for practical purposes unchanged. If every step has been scientifically correct we have at the end very nearly the fresh fish we had to start with. But there is the rub. At every turn it is possible to depart from the scientifically correct. The principles of osmosis here very briefly stated are the fundamentals of the art of salting fish. In all that follows there will be frequent occasion to refer to osmosis. ”

“ This principle of osmosis is of almost universal application in nature and is used by men in the arts, but a good understanding of it is not common. By osmosis our food is taken from the intestines to the blood without any communicating opening. ”

“ All the substances which were capable of producing osmotic membranes by mutual contact sprang into growth,—the soluble salts of calcium, carbonates, phosphates, silicates, albuminoid matter, became organized as osmotic productions,—were born, developed, evolved, dissociated, and died. Millions of ephemeral forms must have succeeded one another in the natural evolution of that age, when the living world was represented by matter thus organized by osmosis. ”

“ Again Bancroft has shown that the pressure for finite solutions in osmosis varies with the heat of dilution, which again varies with the specific nature of the solvent and the solute. [43] All this brings us back to Gibbs's fundamental position that osmotic pressure "is a function of the temperature and the n potentials. [44] From this point of view, Graham's original doctrine, that osmosis is the conversion of chemical affinity into mechanical power, [45] is at once true to the mathematical theory and the laboratory facts. ”

“ If you substitute solid particles, or things that will not dissolve, you will find no change. This property which membranes, such as a bladder, have, is called osmosis. It is by osmosis chiefly that the raw, nourishing material in the blood gets into the flesh lying about the capillaries. It is by osmosis chiefly that food gets out of the stomach into the blood. It is by this property that the worn-out materials are drained away from the blood, and so cast out of the body. By osmosis the blood nourishes and purifies the flesh. By osmosis the blood is itself nourished and kept pure. ”

“ When we see under our own eyes the cells of calcium become organized, develop and grow in close imitation of the forms of life, we cannot doubt that such a transformation has often occurred in the past history of our planet, and the conviction becomes irresistible {172}that osmosis has played a predominant rôle in the history of our earth and its inhabitants. It is a matter of astonishment that the scientist has taken no notice of the active part which osmosis has played in the evolution of our earth. ”

“ Well, when a man of his age—he'd be near fifty—begins to ask questions, he's rather worse than a child who wants to know where Heaven is or some such thing—for you can't put him off as you can the child. Somewhere or other he'd picked up the word "osmosis," and seemed to have some glimmering of its meaning. He dropped the molecules, and began to ask me about osmosis.
"It means, doesn't it," he demanded, "that liquids will work their way into one another—through a bladder or something? Say a thick fluid and a thin: you'll find some of the thick in the thin, and the thin in the thick?" ”

“ The phenomena of osmosis are naturally of the first importance in the action of organisms, and for a long time have attracted the attention of naturalists. De Vries imagined that the contractions noticed in the protoplasm of cells placed in saline solutions were due to a phenomenon of osmosis, and, upon examining more closely certain peculiarities of cell life, various scholars have demonstrated that living cells are enclosed in membranes permeable to certain substances and entirely impermeable to others. ”

“ Osmosis, the passing of liquids through a porous partition and their diffusion, is due to the capillary attraction in the pores of the partition, and to the attraction which exists between the particles of the fluids. The force of attraction, varying with different fluids, seeks equilibrium, and attains it by diffusion. ”

“ The resemblance between an osmotic growth and a living organism is much closer than that between a living being and a crystal, there being not only an analogy of form, but also of structure and of function. In order to find the physical parallel to life, we must turn to osmosis and osmotic growth rather than to crystals and crystallization.
The first and most striking analogy between living beings and osmotic growths is that of form. The morphogenic power of osmosis gives rise to an infinite variety of forms. An osmotic growth, even at the first sight, suggests the idea of a living thing. ”

“ It was observed, however, that the acids contained in the puer diffused through the membrane; this was shown by the addition of a few drops of phenolphthalein to the lime solution, when the pink colour disappeared after a short time in the neighbourhood of the skin. These phenomena are due to osmosis. It is the fundamental property of all animal membranes, to allow some substances to pass through them more easily than others. ”

“ Here are proper conditions for osmosis, and this process of dialysis will take place whenever the intestinal contents holds more dialyzable material than the blood. Under these conditions, which will always occur after food has been digested by the digestive juices, the food will begin to pass through this membranous wall of the intestine into the blood under the influence of the physical force of osmosis. Thus the primary factor in food absorption is a physical one. ”

“ Osmosis comes into play in "floating," as he further points out: "By this process the body of the oyster af [92] fects a plumpness and largeness which materially increases its selling qualities, as it increases its weight and size and, therefore, the profits of the dealer. ”

“ Each bend produced by it while yet the tissue is undifferentiated, squeezes towards the place of growth and evaporation the liquids that are passing by osmosis from cell to cell; and when the lines of movement become defined, each bend helps, by forcing the liquid along these lines, to remove obstructions and make continuous canals. As fast as this transfer of sap is facilitated, so fast is the plant enabled further to raise itself, and add to its assimilating surfaces; and so fast do the transverse strains, becoming greater, give more efficient aid. ”

“ A still more interesting series of examples is afforded by the passage of gases through partitions of metal, notably the passage of hydrogen through platinum and palladium at high temperatures. When the process is considered with reference to a membrane or partition taken as a whole, the passage of a substance from one side to the other is commonly known as “osmosis” or “transpiration” (see Solution) , but what occurs in the material of the membrane itself is correctly described as diffusion.
Simple cases of diffusion are easily observed qualitatively. ”

“ Diffusion is not equal or alike in all cases; it depends upon the extent to which the two liquids are diffusible, upon their different densities, upon temperature, and a variety of other conditions. So, in the case of osmosis, we have not only the nature of the two fluids to consider, but their relation to the [165] membrane that separates them. The membrane may be much more permeable to one of the two fluids than to the other. Thus, in the case of a living cell, the membrane or wall is much more permeable to water than it is to protoplasm ”

“ Oxygen and food materials, which are found in great abundance in the blood, are less abundant in the lymph and still less abundant in the cells. According to the principle of osmosis, the main flow of oxygen and food is from the capillaries toward the cells. On the other hand, the wastes are most abundant in the cells where they are formed, less abundant in the lymph, and least abundant in the blood. Hence the wastes flow from the cells toward the capillaries. ”

“ Calcium chloride, for example, growing in a solution of potassium {130}carbonate, is transformed into calcium carbonate. CaCl2 + K2CO3 = CaCO3 + 2KCl. Thus an osmotic growth can make a choice between the substances offered to it, rejecting the potassium of the nutrient liquid, and absorbing water and the radical CO3, while at the same time it eliminates and excretes {131}chlorine, which may be found in the nutrient liquid after the reaction.
Of all the ordinary physical forces, osmotic pressure and osmosis alone appear to possess this remarkable power of organization and morphogenesis. ”

“ An osmotic growth has a temperature above its medium, since the chemical reaction of which it is the seat is accompanied by the production of heat. We know {154}but little of the transformation of energy which takes place in an osmotic production, but we may say with certainty that it is capable of transforming both chemical energy and osmotic energy into heat and mechanical motion.
An osmotic production is the arena of complicated chemical phenomena which produce a veritable metabolism. It has long been known that diffusion and osmosis may determine various chemical transformations. ”

“ This inflow is called endosmosis, and the outflow of the solution is called exosmosis. If an indiarubber bottle be filled with water and immersed in alcohol or ether, the endosmosis of the spirit will be so powerfully exerted as to distend the bottle considerably. If the bottle be filled with alcohol or ether, and surrounded by water, it will nearly empty itself.
The force exerted by this action is displayed by the rising of the sap from the rootlets of a forest giant to the cells of its topmost leaves. Not only plants, but animals also, are complex osmotic machines. ”

“ The importance of the osmotic pressure of sea-water in biology will be easily understood from the fact that a frog placed in sea-water loses water by exosmosis and soon becomes 20% lighter than its original weight, while a true salt-water fish suddenly transferred to fresh water gains water by endosmosis, swells up and quickly succumbs. The elevation of the boiling point is of little practical importance, but the reduction of vapour pressure means that sea-water evaporates more slowly than fresh water, and the more slowly the higher the salinity. ”

“ Tensions often arise in the plant, and do work expressed as movements—e.g. the springing of elastic Balsam fruits, stamens of Parietaria, etc.
Osmotic energy not only results in enormous pressures and tensions, but causes movements by diffusion and diosmosis, and any given osmotic substance which carries this energy with it is not necessarily formed always in the same way in the cell—e.g. glucose may arise from starch, or from carbon-dioxide, or from oil. ”

“ Plants absorb their food entirely in a liquid or gaseous form, by imbibition, according to the law of endosmosis, through the walls of the cells that form the surface; as when liquids of unequal density are separated by a permeable membrane, the lighter liquid or the weaker solution will flow into the stronger with a force proportionate to the difference in density ”

“ It seems equally reasonable to believe that osmose would take place through both the outer coating of the body and the cell-walls of the animal's body. As long as the oyster stays in the salt water, the solution of salts within its body would naturally be in equilibrium with the water outside. When the animal is brought into fresh or brackish water, i. e., into a more dilute solution, we should expect the salts in the more concentrated solution within its body to pass out, and a larger amount of fresh water to enter, and produce just such a distention as actually takes place in the floating. ”