In the stomach, sugars are changed by the _Bacterium acidi lactici_ into lactic acid, which is further split into butyric acid, carbonic acid gas, and hydrogen. Succinic acid and other substances are also formed. This occurs in the first stage of gastric digestion. When a considerable quantity of hydrochloric acid has been poured out, lactic fermentation is stopped. The small amount of gaseous products formed normally is of little consequence; but flatulence is a most annoying symptom of indigestion. “Put your trust in Providence, and you will feel more cheerful after luncheon,” Dr. Jowett is alleged to have remarked to a despondent friend. The presence of food stimulates the stomach to contraction. Accumulated gases are expelled. Hydrochloric acid is secreted, and puts a stop to fermentation for a time. But if the meal be too heavy or the mucous membrane in an irritable condition, the contents of the stomach become unduly acid in the later stages of digestion. Other bacteria then develop, leading to fresh trouble; more gases accumulate, and the dyspeptic’s distress is greater than it was before. Unfortunately, antiseptics, such as creosote, and carminatives, such as oil of lavender, oil of peppermint, or alcohol, which for the moment give relief, increase irritability, and consequently in the long-run make matters worse. It is the fermentation of the later stages of digestion which causes most annoyance. Admirable as was the Master of Balliol’s advice, it hardly took account of the fact that bacteria which cause flatulence, with its resultant feeling of oppression, are derived for the most part from the imperfectly digested, and therefore actively fermenting, remnants of food which were present in the stomach when the meal was taken. It would be far beyond the scope of this book to consider the pathology of dyspepsia; but the study of normal conditions reveals the fact that some amount of fermentation invariably occurs. The _Bacterium acidi lactici_ is always present in the stomach. Normally its activity is arrested by the hydrochloric acid of the gastric juice about twenty minutes after a meal. After this no further multiplication of bacteria should occur. The presence of bacteria which grow in a strongly acid medium usually indicates that the stomach was not completely emptied before fresh food reached it. It may be that the last meal was too large or the interval too short. If the mucous membrane is in an unhealthy condition, its own secretions afford material on which bacteria thrive. Nothing short of washing it out with a stomach-pump will clean it up. The presence, at the time of feeding, of food left over from the previous meal is likely to perpetuate the unsatisfactory state of affairs. All the glands of the alimentary tract exhibit a tendency to periodicity. Their efficiency is greatest when activity follows a period of rest. If the stomach is not able to expel its contents, it has not the opportunity of preparing for fresh duties.