Absorption in the Animal Kingdom, although performed upon the same general principles, and being adapted to attain the lame general ends, presents more various modifications of form and greater com plication than in the vegetable kingdom. In the first place, the nature of the fluids taken up differs, more especially in the class of cases where that function is adapted to nutrition. Plants derive their food from the mineral kingdom. Animals obtain their food from plants. Planta live on carbonic acid, ammonia, water, and various salts. Animals live on substances elaborated out of these compounds in the cells of plants. In the next place, animals receive their food into an interior sac or bag called a stomach, whilst plants pinnge their absorbent cells into the soil from which they derive their nutriment In the higher forms of animals, a system of vessels called absorbents [AnsoeuExr SYsrest] is made subservient to the ends of the function of absorption—an arrangement which is found nowhere to exist in the vegetable kingdom. In the lower animals, as in the sponges and some of the infusoria, the function of absorption is performed by contiguous cells almost as simply as in plants. In certain parts also of the higher animals, we have absorption carried on in the same way as in the cells of cartilage, and in the contiguous cells of the mucous and cutaneous membranes. In none of the invertebrate animals have we any special absorbent system nt alL In the animal kingdom the circulating system has the power of absorption in even a greater degree than the absorbents themselves. From the structure of the walls of the veins, arteries, and capillaries, and the knowledge of the fact that there is constantly passing through them a demise liquid—the blood—we should expect that these organs would offer the uecessaryconditioiis for absorp tion. This has been proved by direct experiment. Tiedemaun and amain found that when such substances as gamboge, madder, camphor, musk, and assaftetida, which are easily detected by their colour and odour, were introduced with the food into the stomach, they were seldom found in the chyle in the time that they itad found their way into the Wood, and some of them even into the urine. It was also found that if poisonous substance. were introduced into the intestines, and secured in one place by two ligatures, and every other part cut away but the artery and vein, they exerted the same influence on the system, and in the same time as usual; whilst if the intestine was treated in the same manner, and all parts cut away but the lacteals, the evidences of absorption were deferred for a much longer period than usuaL From these experiments and others it would appear that the 1actesde are adapted for receiving only n certain class of compounds, more especially of an oleaginous and albuminous kituL That part of the absorbent system called Lyinphaties were at one time *Imposed to be engaged in conveying to the blood the used-up matters from all parts of the body preparatory to their final expulsion from the system. The nature,hoaevcr,of the clear fluid lymph which
is contained in them 110(44 not support this opinion, and as this lymph has a composition very like to the blood without its red corpuscles, it is inferred that the office of the lymphatics is to assist in the preparation of materiels for the blood. These materials being scattered all over those parts of the system on which the lymphatics; are distributed, it in to the blood-vessels that the office must be wattled of taking up effete matter, and carrying it into the blood.
That the general cutaneous and mucous surfaces of the body will both exhale and absorb, are well-known facts. The akin, through its perepiriferous glands, which perform their function through the agency of cells, exhales moisture, whilst it is also a powerful abaorbent surfaco.
It is proved by direct experiment, that the human hand is capable of imbibing, in a quarter of an hour, an ounce and a half of warm water, which, for the whole body, is at the rate of six or seven pounds per hour. An interesting narrative Is on record of a ship's crew who were exposed at sea for seventh days in an open boat; they had connumel oil their water ; they bad no fluid of any kind which they could drink; they soon level to suffer from thirst; the feeling at length became intolerable, and the drinking of sea-water was found only to Increase its intensity. When nearly exhausted, they were exposed., during several hours, to a heavy shower of rain. As soon as their clothes became thoroughly wet their thirst began to abate, and before the rain had ceased their thirst was gone. They did not fail to profit by this experience. From this time each man, as soon as he began to feel thirsty, dipped his shirt in the sea-water and wore it next his akin, which had invariably the effect of removing his thirst, the absorbents taking up the particles of water, but rejecting the saline matter dissolved in it. The mucous surface of the lungs is con stantly engaged in throwing off the vapour of water and carbonic acid, and absorbing oxygen gas. It is also threep), the pulmonary surface that poisons are introduced into the blood, which result in the production of disease, as small-pox, measles, scarlet fever, and others. The different relations of absorbing surfaces to poisonous substances is an interesting subject Thus, poisons which may be introduced with impunity into the stomach will destroy life when applied to the minutest wound in the skin, as in the case of the poison of venomous serpents, and the Woorara poison. This has been proved not to depend on any decomposition taking place upon the surface of particular membranes, as the Woomm has been introduced into the stomach and bladder, and when rejected has been found to retain its primitive destructive power.