This occurs in almost every case, and is responsible for many of the symptoms of dyspepsia. It is a constant phenomenon in stenosis of the pylorus, but comparatively infrequent when the cardiac orifice is obstructed. The special symptoms to which it gives rise vary greatly in severity. In some cases the patient merely experiences a certain amount of fulness and discomfort after meals, which are relieved by eructation, while in others painful distension of the abdomen and frequent belchings of gas persist for hours. Although it is usually increased by food, it is also troublesome in the intervals of digestion, and is particularly distressing during the night. Sometimes a sense of thoracic constriction amounting to severe pain ensues upon the slightest exertion, while at other times the upward displacement of the heart induces violent palpitation, throbbing in the head, or vertigo. Occasionally syncope or pain like that of angina pectoris occurs, or asthmatic attacks supervene after meals, accompanied by extreme breathlessness and cyanosis. Hot flushes, with headache, confusion of thought, somnolence and hiccough, also constitute a frequent source of complaint. Under normal circumstances the gaseous contents of the stomach consist of air which has been swallowed and. a variable quantity of carbon dioxide, derived from the blood or from food-fermentation. The chyme itself, when removed from the stomach, exhibits very slight gas formation for several days, owing to the presence of hydrochloric acid, which controls the natural tendency to putrefaction. When, however, obstruction of the pylorus or inefficient peristalsis has delayed the transmission of food into the bowel, fermentation invariably occurs, and leads to the production of a considerable quantity of gas. This process can readily be studied and its activity estimated by filling a test-tube of medium size with the semi-digested food withdrawn by a tube, and inverting it over a small cup or glass beaker partially filled with the same material. If any gas is evolved it will collect at the upper part of the tube, where it can be roughly estimated by the amount of depression of the liquid column. When the digestive process is healthy little or no gas is observed at the end of three hours, but in cases of gastric dilatation a sufficient quantity may be formed in that time to occupy from half an inch to two inches of the tube. This evidence of excessive fermentation, if combined with an absence of free hydrochloric acid and an excess of lactic acid, constitutes valuable confirmatory evidence of malignant disease of the stomach. The gas collected in this manner or which is eructated by the patient consists approximately of nitrogen (33-47 per cent.), carbon dioxide (13-26 per cent.), hydrogen (21-32 per cent.), and oxygen (6-12 per cent.), with a variable quantity of marsh gas and of sulphuretted hydrogen.

Carbonic acid gas is chiefly derived from carbohydrate fermentation, and especially from that which converts lactic acid into butyric acid; but it may also be formed during the process of alcoholic fermentation. Hydrogen occurs as a byproduct in the manufacture of butyric acid ; while the nitrogen and oxygen are introduced into the stomach in the air which is swallowed with the food and saliva. The coexistence of marsh gas and hydrogen renders the gas inflammable. This was first demonstrated by Hoppe Seyler and Kuhn, and has since been investigated by Van Tieghem, M'Naught, Ewald, and others. It would appear that marsh gas is rarely generated in the stomach, but frequently regurgitates from the intestine in cases of incompetency of the pylorus. The presence of sulphuretted hydrogen may be explained in a similar manner, although there is reason to believe that this gas is occasionally produced in the stomach itself.