ABSORPTION 37 tion and reciprocal interchange of fluids has been shown to take place with the greatest ac- tivity; for the capillary blood vessels here form an exceedingly intricate and abundant network embracing the adjacent follicles and ducts of the glandular tissue, while these ducts and follicles themselves are arranged in a sys- tem of minute ramifying tubes and cavities, penetrating everywhere through the glandular substance. Thus the union and interlacement of the glandular membrane on the one hand and of the blood vessels on the other becomes exceedingly extensive ; and the ingredients of the blood are instantly subjected, over a very large surface, to the influence of the glandular membrane, or the fluids which it has absorbed. The rapidity of transudation under these condi- tions has been shown by the experiments of Claude Bernard and other observers. If a solu- tion of iodide of potassium be injected into the duct of the parotid gland on one side, in a liv- ing animal, the saliva discharged by the cor- responding gland on the opposite side is im- mediately afterward found to contain iodine. During the few instants required to perform this operation, therefore, the iodine in solution must have been taken up by the glandular membrane on one side, absorbed from it by the blood, carried by the blood to the heart, again distributed over the body, absorbed from the blood by the glandular membrane of the second gland, and thence discharged with the saliva. It is by this process that all the nutri- tious elements of the food and drink are taken up from the intestine and finally reach the tis- sues which they are to nourish. They are ab- sorbed from the cavity of the intestine first by its lining membrane ; thence by the blood ves- sels and the blood contained in them; then transported by the circulation to the distant organs and tissues; and finally absorbed by these tissues from the blood, and united with their own substance. But as each tissue has a special power of its own of absorbing certain materials in preference to others, the same blood will supply its materials to each in dif- ferent quantities. Thus the bones absorb from the blood a large proportion of calcareous mat- ter, the cartilages a smaller quantity, and the muscles still less. The brain, on the other hand, takes up more water than the muscles, and the muscles more than the bones. Thus every tissue is enabled to maintain its own pe- culiar constitution, though all are supplied with the necessary ingredients from the same nutri- tious fluid. It is now universally acknowl- edged that the action of drugs, medicines, and poisons takes place in the same way. This ac- tion is sometimes said to be local, as where the ingredients of a blister are absorbed by the skin and produce an inflammation of the in- tegument at that spot only; or general, as where opium when introduced into the stom- ach produces drowsiness or insensibility over the whole body. But in both cases the pro- cess is essentially similar. The opium is dis- solved by the liquids of the stomach, absorbed by its lining membrane, taken up by the blood, and distributed by the circulation all over the body. In this way reaching the brain, it is absorbed by the cerebral substance, and by its action upon the nervous matter causes the narcotism and insensibility which are manifested throughout the system. Thus the general action of an opiate is undoubtedly due to its local action upon the brain, and to the fact that the brain itself, through the ner- vous ramifications, influences the condition of the whole body. II. Absorption of Gases by Solids and Liquids* There are not only porous substances, as earth, charcoal, and animal mem- branes, which will absorb gases, but solid metals will in many instances do the same. Thus re- cent experiments have demonstrated the exist- ence of gaseous hydrogen in meteorites falling on the earth, absorbed by them in their wan- derings through space, perhaps while passing through some nebula, which the spectroscope has shown to consist of incandescent hydrogen ; they bring thence this nebular hydrogen to our earth. The power to absorb hydrogen is espe- cially possessed in a high degree by palladium, which takes up nearly 643 times its own vol- ume of this gas, as proved by Graham, while silver and platinum absorb oxygen, titanium nitrogen, &c. This absorption of gas by metals is called occlusion. Deville and Troost have proved the remarkable fact that red-hot iron and platinum have such a great capacity of absorbing hydrogen, that it passes through these metals as it were through a sieve. The absorption of gases by liquids is still more strik- ing. Water absorbs different gases and holds them in solution, in quantities varying in pro- portion to the nature of the gas. Thus, at a temperature of a few degrees above the freez- ing point, it contains when exposed to the air 4 per cent, in volume of oxygen and 2 per cent, of nitrogen ; so that the air contained in water is much richer in oxygen than our atmosphere, having in six parts four of oxygen, while the atmosphere contains only one part of oxygen in five of air. The solubility of hydrogen in water is equal to that of nitrogen; while in regard to other gases, one part of water in bulk dissolves under the same circumstances 1-3 parts of laughing gas, 1'8 carbonic acid, 3 of chlorine, 4*4 of sulphide of hydrogen, 54 of sulphurous acid, 505 of hydrochloric acid, and not less than 1,180 of ammonia. A rise of temperature of some 70 diminishes this power of absorption to about one half, while at the temperature of the boiling point of water most absorbed gases are expelled. With a dimin- ished pressure of say half an atmosphere, about half the gas is expelled ; while at an increased pressure of say two atmospheres, more gas can be absorbed. Thus in respect of carbonic acid, for instance, every atmosphere pressure aug- ments the capacity of water to absorb this gas by 1 -8 volumes, so that at five atmospheres it ab- sorbs nine tunes its own volume of the same.
