This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
When the gastric mucous membrane is morbidly sensitive and irritable, carbonic acid gas dissolved in water is an excellent sedative, and in uncomplicated cases is sufficient to relieve vomiting. It is commonly given in combination with an alkali, as in the ordinary effervescent mixture, or in the waters of Homburg, Carlsbad, Vichy, etc., but water charged with the gas only, often answers exceedingly well, and has sometimes cured intense gastric irritation (chronic in character with great nerve-depression) after the failure of treatment at celebrated Spas.
There are other virtues attributed to carbonic acid, which are not so well ascertained. Thus, Dr. Parkin and Dr. Ritson argued that the freedom of many ports from cholera was traceable to the increased amount of carbonic acid in the atmosphere of their coal works and wharves! (Lancet, ii., 1848).