Description and Properties. - Colorless, transparent, cubical crystals, or a white, crystalline powder, odorless, and having a purely saline taste. Permanent in dry air. Soluble in 2.8 parts of water at 250 C. (770 F.), and in 2.5 parts of boiling water; almost insoluble in alcohol.

It should contain, when dried, not less than 99 per cent. of pure sodium chloride.

Average Dose. - Emetic, 240 grains (16 Gm.).

Sodium chloride, NaCl, although rarely given by way of the stomach, save as an emetic, plays such an important role in intravenous injections for the relief of shock, and is, moreover, so important a constituent of the body fluids, that it deserves consideration. The physical phenomena connected with its absorption and action are typical of a class of actions constantly going on in the physiological processes of the body and as such are properly treated in a work on Physiology.

Therapeutics. - Local Action. - Weak salt solutions applied to the skin penetrate the superficial layers. These become swollen. Stronger solutions, by tending to draw water from the tissues, are irritants - particularly to mucous membranes. Both salt and water may be absorbed through mucous membranes; but neither are taken in to any great extent by the skin. On the mucous membrane of the mouth, weak (hypotonic solutions) cause a slight swelling of the epithelium, while strong solutions are irritant, withdrawing water, and often inducing nausea and vomiting. Digestion is not markedly affected by small doses - indeed, the effects on taste may be said to be helpful to good digestion.

Internally. - Salt in weak solution is not known to induce any marked physiological reactions when taken by the mouth. When injected intravenously in strong solutions in animals death has been known to occur by reason of its action on the nervous system possibly because of its disturbance of water pressure in the nerve cells. Death in these cases is usually preceded by symptoms of lassitude, increased reflex excitability, and convulsions. Circulation is not known to be affected, save in the late stages. Blood changes are usually present. They consist, as a rule, of agglutination of the red blood cells with formation of capillary thrombi. With isotonic solutions no such results occur.

Certain effects on the blood are usually present even when the salt solution is absorbed through the intestinal walls. Very weak solutions bring about a condition of hydremia of the blood, whereas a reverse condition may follow the use of comparatively strong solutions of salt 1-2 per cent. The various intricacies of the reactions of lymph flow and blood flow have little place here, although of vital importance as biological, if not pharmacological, data.

The action of isotonic salt solution given by the rectum is of particular moment, since this is the avenue by which it is most frequently introduced. In anemic subjects the solution is absorbed with great rapidity, and the volume of the blood, particularly following its diminution from hemorrhage, rapidly increases. The blood-vessels become fuller; the vascular tone rises, the heart action becomes stronger, and bleeding patients at times in a semicomatose condition frequently may be brought out of their lethargy.

Saline solution thus introduced has a very marked diuretic action, particularly if the element of heat be added. The increase in the flow of urine is due in large part to the increase in the amount of fluid in the vessels, resulting in an increase in tension in the capillaries. The chlorides, and the potassium and sodium of the urine, are eliminated in larger quantities than are the sulphates,phosphates, or urates, but practically all of these are increased in amount.

See Schaefer, Text-Book of Physiology.

Tissue metabolism is stimulated by the use of salt, although certain investigators have thought that there results from its use a slight diminution in proteid catabolism. The general action is, however, one of increased lymphatic activity.

So far as salt baths are concerned, the effects, while they may be very beneficial, are not resident in the salt, so far as its absorption into the body is concerned. Hygienic, dietetic, and psychotherapeutic practices are more to the point in the treatment of patients at spas and watering places than the salts contained in the bathing water. As an irritant to the skin salt action is beneficial. It tones and invigorates the skin and thus, reflexly, the patient in general.

Salt when taken by the mouth is often very useful. It exerts a mild stimulating action on the gastric mucosa, and in combination with sulphates and other acids and salts is an essential element in all of the mineral waters, which will be discussed later.

Taken by the rectum (enteroclysis) or by the skin (hypodermo-clysis) isotonic salt solutions are invaluable in the treatment of collapse conditions due to hemorrhage, to cholera, to dysentery, and often to the toxemias of the infectious diseases, notably diphtheria, typhoid, and pneumonia. Clinical evidence is certain as to the value of isotonic salt in solution for surgical shock, particularly when administered hot - 112-118 F. As a diuretic in kidney affections hot saline enemata are invaluable.