ABSORPTION (ante). All the membranes and tissues of living bodies have the prop erty of absorbing fluids—a property that continues after death and until decomposition. In absorptions in animal organisms fluids do not penetrate tissues mechanically through orifices, for the existence of such orifices, or open mouths, once taken for granted, has been disproved by late microscopic research. It may therefore be surmised that absorp tion is equivalent to molecular combination of organs or tissues and fluids or things absorbed. Animal substances differ in absorbing power with difference in liquids, taking, for example. 100 parts of clear water and only 65 of brine, and less if the brine be stronger; and a tissue taking 100 parts of brine will not receive a quarter as much of an oily liquid. An idea of differences may be got from Chevreul's table: Activity of absorption varies with the freshness of the membrane, being most the soonest after separation from the principal parts; and varies also with pressure, motion, and temperature. Absorption of oxygen by the blood in the lungs is apparently instantaneous, the change in color from blue to red as soon as it arrives at the pulmonary vessels show. ing the action of the gas it has taken from the atmosphere. This rapidity of absorption is due to the diffusion of the blood in a great number of minute channels, whereby the vascutar and absorbing surfaces are brought into contact over a large surface; and to the incessant motion of the fluid, by which its effects become perceptible at the earliest pos. sible time. Claude Bernard found that if a solution of iodide of potassium were injected into the duct of the parotid gland on one side of a living animal, the saliva discharged by the corresponding gland on the other side almost instantly afterwards contained Iodine. In a measureless instant, therefore, the iodine was taken up by the glandular membrane on one side, absorbed by the blood, carried to the heart, absorbed from the blood by the glandular membrane on the other side, and furnished to the saliva. It is by this process of absorption that the elements of nutrition are taken from the intestines and conveyed to the tissues they-are to nourish; the bones absorb much calcareous matter from the blood. cartilages less, and muscles less still; the brain takes more water than does muscle, and muscle more than bone. Late medical schools agree that the action of drugs and poisons takes the same course. Opium dissolved by the liquids of the stomach is absorbed by the membraneous lining, taken away hy the blood and distributed well through the body; at the brain it is absorbed by the cerebral substance, nets upon the nervous matter, and produces narcotism or insensibility, and the brain, through its nervous ramifications, affects the whole body. The quickness of absorptive action is shown in using hypoder mic injections: almost before the syringe has punctured the skin of the forearm a severe pain iirtlie foot is sensibly relieved. Absorption of Gases by id metals will some
times absorb gases. Gaseous hydrogen has been found in newly-fallen meteorites, obtained perhaps while passing through nebulte. Palladium will take 643 times its own volume of hydrogen; silver and platinum absorb oxygen; titanium takes nitrogen; hydrogen will pass through platinum and red-hot iron like water through a sieve. Liquids rapidly absorb gases; water near the freezing point contains in volume 4 per cent of oxygen and 2 per cent of uitrogeu, equal to 4 oxygen in 6 parts, while air has only 1 oxygen in 5 parts. At the temperature of 70' the power of absorption is reduced to one half, and at boiling nearly all absorbed gases are thrown off. Under low pressure less and under high pressure more gas can be taken in. Solutions of neutral salts absorb about the same amount as water, except sulphates; acids absorb least, dilute sulphuric taking less titan a quarter of one per cent in volume. Absorption of Ikal. —The. capacity of substances for absorbing heat varies widely; it is least in smoothly polished or bright and light col ored objects; greatest in dark colored and rough surfaces. It is found in regard to color, that more depends on the coloring material than on the color itself. When the heat giving body is non-luminous, color is without influence, but great in case of luminous bodies. gilere are also great differences in the absorbing power of transparent sub stances; rock-salt absorbs only 8 per cent of the heat passing through with the light, fluor spar 25 to 50 per cent, Iceland spar and glass 60 per cent, alum 90 per cent, and ice 94 per cent. These substances transmit the heat which they do not absorb. Absorption of Light is the process which takes place when light enters an imperfectly transparent medium, a portion of the light being stitled or spent in producing some physical effect, while the remainder is either directly transmitted or after one or more internal reflections.
A body absorbing all the light that reaches it would be perfectly black and wholly invisible; but in point of fact the blackest object reflects some light from its surface. A body absorbing none but reflecting all light would be perfectly white. In general the different parts of white light arc absorbed with unequal energy, and thus the light which escapes absorption is colored. In most cases the colors of natural bodies arc occasioned in this t way. Transparent substances absorb light in varying degrees, and in many of them an elective absorption takes place; glass, gems or liquids absorb certain colors and let others pass, those which pass determining the coldr of the substance. Occasionally a color com plementary to one absorbed is reflected, as red rays transmitted from red aniline and green rays reflected. Certain crystals are polychromatic, showing changing colors as light passes through in different directions.