The alkalies and their combinations with acids, forming salts, act in the system in a different way from the animal or vegetable drugs or the metals. When the salts are taken into the stomach and intestines there is set up a process of osmosis, diffusion, and filtration, while the secretory activity of the mucous-membrane cells in these organs is increased, and, as a result of these various actions, water is diverted from the blood into the stomach and intestines, at the same time that a portion of the salt is absorbed. Later the fluid and salt are all absorbed in the case of the chlorides, iodides, and bromides, this being accomplished readily. The carbonates, tartrates, citrates, phosphates, and sulphates are less readily absorbed, the last two being very difficult of absorption. The alkalies also vary in their rate of absorption, magnesium being very difficult of absorption. This enables one to understand why magnesium sulphate (Epsom salt) is a good purgative.
The following list shows the rate of absorption of the various alkalies and salts, those most rapidly absorbed being given first, the rate decreasing in order as given:
The action of the saline purgatives is considered to take place in this manner: When the salt enters the stomach and passes into the intestines, very little if any of it is absorbed, but a great deal of water is extracted from the blood by osmosis, diffusion, and filtration. This distends the intestines, increases peristalsis, and the contents of the bowel is liquefied and evacuated. The blood then repletes itself from the tissues. Should the blood and tissues be deficient in fluid this process would not go on, and there would be no purgative action. The salt would be slowly absorbed and cause diuresis, with consequent greater decrease in the fluid of the blood. But in cases of dropsy the fluid will be drawn off and evacuated through the bowel. The saline purgatives should be given in the morning, on an empty stomach, in as little water as will dissolve the salt, the water being as hot as can be taken internally. Activity aids the action of the salines, therefore the person taking them should move about during the day if practicable. The three alkalies, sodium, potassium, and ammonium, with their salts, may be divided into four groups.
1. In this group are placed sodium chloride and potassium chloride, which exhibit the specific action of the metallic ions, sodium and potassium, and are therefore depressant.
II. Group two contains sodium and potassium hydroxide, carbonate, and subcarbonate, which act through the non-metallic ion (the hydroxide, carbonate, or subcarbonate) by deoxydizing, or drawing oxygen from, the tissues. Their action is manifested in three ways: They
1. Neutralize acids, stop stomach secretion, aid pancreatic secretion, and cause alkaline urine. Some claim that they stimulate stomach secretion by neutralizing acid.
2. Dissolve proteids, and change them to alkali pro-teids - surface effect on skin and mucous membrane.
3. Saponify fats - surface of body and alimentary canal.
III. Ammonium chloride represents this group. Its action is due to both the metallic and non-metallic ion. It is stimulant and is used as an expectorant.
IV. Ammonium hydroxide and carbonate belong to this group, which is noted for its instability. Ammonia is given off freely and readily, exhibiting its stimulant effect. "Smelling salts" and aromatic spirits of ammonia belong here.
Salt action is not confined to the alkalies and salts, but is possessed by other bodies, such as sugar and urea.