SODIUM, SALTS OF. Sodium is a soft, silvery white metal, the salts of which are employed in medicine to some extent. Most of these salts act in a manner similar to those of PorAssium (which see), although to a somewhat milder degree. Sodium carbonate is the common washing-soda of commerce. Sodium bicarbonate, or baking-soda, is derived by the action of carbon dioxide on sodium carbonate, and occurs as a white, crystal line, compound powder. Mixed with an acid substance, as cream of tartar, it is used in cookery for raising cake, etc. Its chief use in medicine is as an antacid in cases of gastric acid ity giving rise to belching or flatulence.
The dose is half a teaspoonful or more, given in a glass of water. Sodium hypophosphite occurs in small, clear crystals. It is used together with other hypophosphites in a compound syrup, and is also given alone in some cases of nervous disturbances. Sodium bromide is used as a nerve-sedative. Sodium salicylate is of importance in the treatment of rheumatism, gout, etc., and is used also as an intestinal disinfectant.
Sodium chloride, or common salt, does not pass easily through a mem brane. If, therefore, blood-cells are placed in a solution containing more salt than the normal fluid of the blood, the cells will give up some of their water, and shrink in size. If, on the other hand, the solution contains less salt than normal blood-serum, the cells will take up water from the solution, swelling up and becoming globular. A watery solution of salt which is isotonic with blood-serum and blood-cells is called a normal salt-solution. Such a solution is about per cent. in strength, and in it body-cells can retain their form and vitality. Plain water or a concentrated solution of salt, for the reasons given above, prove irritating to exposed tissues ; while a normal salt-solution serves as a very bland, unirritating wash. Sodium chloride has practically no effect on the tissues other than this physical action. Normal salt solution can therefore be injected into the veins in large quantities without any untoward effects. This fact is utilised when it is desired to increase the amount of fluid in the body rapidly, as after severe haemorrhage or in surgical shock, when the blood-pressure is dan gerously low. It may be injected under the skin or given by rectum. It
is used, with or without bleeding, to dilute poisons in the blood and stimu late their excretion, as in urEemia, gas-poisoning, etc. Neither salt nor water is absorbed through the skin, and salt baths are of service merely as they cause a certain amount of reflex stimulation by a slight irritation and by the pressure. Concentrated salt-solution, injected into the rectum, acts efficiently as an enema. A teaspoonful or so taken by mouth acts as an emetic, and is often given in cases of poisoning. The strong solution is efficacious also as an antiseptic wash, especially as a mouth-wash in cases of foul breath.
SOIL, THE.—All living things are composed of substances originally derived from the earth ; and, after death, all the component parts of the organism return to the earth through the processes of decomposition and disintegration. The bacteria of decomposition, which are normally present in the soil, play an important and useful role in breaking up this dead organic material.
Such decaying substances in the soil may, however, exert a harmful in fluence on living human beings by producing exhalations of unhealthy gases, by foul odours, and by poisoning the water intended for household purposes. Under certain circumstances, particular danger may result from the presence of the bacteria of various infectious diseases, such as typhoid, cholera, tetanus, anthrax, etc., which may remain in the superflcial layers of the soil for considerable periods. The living human body may become infected with any one of these diseases, either directly or through the medium of food. The air which is present in the soil may also find its way into human habitations ; and if it be contaminated by poisonous gases, it may constitute a serious menace to health.
In a similar manner, moisture may be communicated to dwellings, the water being absorbed by the walls ; and it is, therefore, very unhealthy to live in houses which are built on damp soil, or which have not been thoroughly dried before being inhabited. In cities, the best way to purify and thoroughly dry out the soil is by a complete system of drains and sewers.