Sodium bicarbonate neutralizes acids and dissolves mucus. According to Pawlow (1897), it tends to inhibit salivary, gastric, and pancreatic secretion. But in Pawlow's laboratory, Sawitch and Zeliony (1913) have demonstrated that when it is applied to the pyloric mucosa it causes acid gastric juice to be secreted by the stomach in general.

The effect of an alkali in the stomach will vary greatly according to the nature of the stomach contents at the time of its administration. In the resting period, sodium bicarbonate merely dissolves mucus and is absorbed as bicarbonate into the blood, to increase its alkalinity directly. In the digestive period it reduces the secretion of gastric juice, neutralizes a portion of the hydrochloric acid, liberates the carminative carbon dioxide gas, and is absorbed as sodium chloride. In cases of fermentation or "sour stomach" it may neutralize the organic acids, and so result in the opening of a spasmodically closed pylorus; while at the same time its Co2 acts to overcome flatulency.

The time of administration must, therefore, be chosen with a definite purpose. Usually for hyperchlorhydria one hour or two hours after meals will be the period of harmful excess of acid. In continuous hyperacidity and in fermentative conditions a dose an hour before meals will tend to prepare the stomach for the next meal; or sometimes a dose will be necessary immediately after eating because of abnormal acid or gas having been present at the commencement of the meal. A dose at bedtime tends to check the early morning acidity, or a dose on arising cleans the stomach of acid and mucus before breakfast. In duodenal ulcer it may be needed when the "empty pain" comes on. In alcoholic gastritis it may be used in solution for lavage to remove excessive thick mucus.

Seelig, Tierney, and Rodenbaugh find that intravenous sodium bicarbonate solutions exert an effect beyond those of other alkalies in raising blood-pressure, and Howell states that a less alkaline state of the blood causes relaxation of the blood-vessels, while an increase in the alkalinity improves their tone. But rapid excretion makes it difficult to produce more than temporary changes in the alkalescence of the blood.

In mild conditions of acidosis the bicarbonate may be given by mouth in quantities to keep the urine only slightly acid. In diabetes, though it favors the excretion of the acetone bodies, its continued use may interfere with the normal acid-neutralizing functions of the body. Underhill found the blood-sugar content of a normal rabbit unaffected by intravenous dilute alkali, but in dogs with hyperglycemia Macleod obtained a distinct lowering of the sugar, and Murlin and Sweet have come to the conclusion that alkalies serve to promote glucose oxidation and to favor the work of the pancreas.

In severe conditions of acidosis, as in diabetic coma, uremia, pneumonia, or delayed chloroform poisoning, enormous doses, up to 1/2 ounce (15 gm.), have been given by mouth; and by rectum, by the continuous drop method, as much as 2 ounces (60 gm.) per day in 3 per cent. solution. In diabetes these amounts, with sodium bicarbonate intravenously in 3.5 to 4 per cent. solution, give only occasional good results (von Noorden); and the reason for this may be that in diabetes there is no change in the alkalinity of the blood as judged by the hydroxyl ions, though in acidosis from mineral acids the blood is acid (Folin). But in the acidosis of uremia the author has successfully employed 1 1/3 ounces (40 gm.) of sodium bicarbonate intravenously in both 4 and 10 per cent. solutions, and there are good reports from its use in the acidosis of pneumonia. Generalized edema, edema of the lungs, and chills are reported following its intravenous use.

In rheumatism and sometimes in gout it is given until the urine is alkaline. Von Noorden believes that in gout alkalies are useless and perhaps harmful. Fauvel states that as much as 1 1/2 ounces (6 gm.) a day has no effect on the excretion of xanthines or uric acid. By increasing the salts of the blood it is diuretic. In some cases it is distinctly laxative.

The other carbonated alkalies have similar actions, but are less employed. Folin suggests that a mixture of sodium, potassium, calcium, and magnesium salts would be better than sodium bicarbonate alone. "Fischer's solution" is hypertonic, is administered intravenously, and consists of 1 per cent. of crystalline sodium carbonate (containing 10 molecules of water) and 1.4 per cent. of sodium chloride. Following Fischer's recent theory of acid as a cause of nephritis, it has been employed in this disease, but neither the theory nor the treatment seems satisfactory.