4. The circulation in the stomach is also so far under our control, as we have already seen. The many substances which stimulate the nerves also redden the surface of the mucous membrane, by dilating the vessels and increasing the local blood flow within physiological limits, such as Alcohol, Ether, Aromatic and Pungent articles (Pepper, Mustard, Capsicum, etc.), and Bitters. Besides these, there are numerous substances of a more powerfully irritant nature which we note chiefly for the purpose of suggesting caution in their employment for other purposes. Arsenic, Iron, Mercury, and indeed the salts of most of the metals: Senega, Digitalis, and Scilla; Colchicum and Veratria, are examples of drugs which are specially apt to derange digestion. On the other hand, the local circulation can be rendered less active by means of Acids; salts of Silver, Zinc, Lead, in small doses; Ergot, Opium, Tannic Acid, and the many vegetable astringents containing it, such as Kino, Catechu, and Cinnamon. These are gastric astringents, and indirectly, therefore, another class of gastric sedatives.

5. The movements of the stomach can be readily modified. The energy of the churning movements increases with the acidity of the chyme, and we can take advantage of this knowledge by administering acids after meals, such as Diluted Nitric, Hydrochloric, or Nitrohydrochloric Acids, which are thus another class of gastric stimulants, sometimes called gastric or stomachic tonics. Specific nervo-muscular stimulants, such as Strychnia, probably act in the same way, as well as the stimulants of the nerves and vessels, especially Ether and Volatile Oils. That powerful excitation of the movements of the stomach which is called emesis or vomiting, will he specially-described in the next chapter.

Per contra, the gastric movements may be directly diminished by Diluted Hydrocyanic Acid, Opium and Morphia, Carbonic Acid and all effervescing drinks; by the Alkalies, which reduce acidity; as well as indirectly by remedies which soothe the nerves and the vessels, as we have seen.

6. "We have already referred to our influence on the contents of the stomach-to the food, and to the acidity of the chyme. The reaction may be neutralised or completely changed by Alkalies or Alkaline earths, which are thus antacids. Beyond these, Charcoal absorbs the gaseous products of digestion; whilst Sulphurous Acid, Sulphites and Hyposulphites, Carbolic Acid, Creasote, the Aromatic Oils, and possibly all Bitters and Vegetable Astringents in some degree correct decomposition-gastric disinfectants. In this connection mention must be made of many antidotes, which act upon poisons in the stomach.

7. Action Of Carminatives

Action Of Carminatives. The effects of Aromatic and Pungent Oils of Alcohol, and Ether, in rousing the nerves of the stomach, in increasing the activity of the gastric circulation, in exciting muscular contraction, and in modifying the contents, have been separately described; and we may add that they probably at the same time relax the cardiac orifice. The result is eructation, and relief of gaseous distention, of cramps and pain, the whole being so striking and complete that these substances have been grouped together under the special name of carminatives (carmino, I soothe). Their effect is, however, more than local. The nervous impressions produced by carminatives spread even beyond the stomach and its sympathetic ganglia to the cord, medulla, and brain, and reflexly to the heart and vessels, and cause general stimulation, both of the bodily and the mental faculties. Carminatives are thus one form of diffusible stimulants.

III. Pathological Relations

Derangement of gastric digestion, or dyspepsia, is probably the most common disorder of the human body, and may be taken to illustrate, in a general way, the rational treatment of diseases of the stomach.

By far the most frequent causes of derangement of the stomach are to be found in the quantity and quality of the food; in its imperfect mastication and insalivation; in deficiency or in excess of fluids, which dilute the gastric juice and check secretion; and in the abuse of alcohol. Certain drugs in common use are also apt to cause indigestion, such as Opium, Arsenic, Iron, Digitalis, and Scilla. Organic disease of the stomach itself necessarily leads to the same result. Excess of the gastric juice is rare. As a rule, the juice is deficient in relation to the amount of food taken, whether from excess of the latter or from absolute diminution in the secretion, for instance, in debility after illness. Again, either the pepsin or the hydrochloric acid may be deficient, or impeded in its special action. Gastric indigestion is occasionally of nervous origin: depressing mental states readily arrest the action of the stomach; and morbid impressions, originating in the liver, intestines, kidneys, or uterus, often have the same effect.

Disorder of the muscular functions of the stomach may also cause dyspepsia. Feebleness of the churning movements leads to imperfect exposure of the food to the action of the juice; feebleness of the expulsive efforts delays the removal of the chyme, excess of which arrests digestion. In other cases, excessive peristalsis hurries the food into the duodenum before the process of gastric digestion has well commenced.

If from any of these or from other causes, the contact of the food and the gastric juice be deficient, the process of digestion becomes disturbed. The secretion, unable to effect complete conversion of the proteids into peptones, produces some partial chemical change in them; the other constituents of the food are also broken up; and-what with the unnatural products, and, in the case of a heavy meal, the excess of peptones themselves-the process of digestion is completely arrested. A decomposition occurs, associated with the formation of organic acids; the sugar, starch, and fat probably become partially changed; and the contents of the stomach are converted-not into the normal chyme, but into a sour, fermenting mass with abundant development of gas. The stomach becomes distended, and the neighbouring organs impeded in their action, especially the heart. The nerves, vessels, and glands of the stomach are irritated by the products, so that the mucous membrane swells; the rosy hue passes into pallor; and the surface is coated with a tenacious mucus. The gastric and associated centres are powerfully excited; and impulses are sent out which lead to hiccup, eructation, and vomiting. If these do not give relief, the contents pass into the bowel, irritate it also by their excessive acidity, and give rise to duodenal dyspepsia and diarrhoea. Even when the urgent symptoms have subsided, the morbid anatomical condition remains for a time associated with an excessive secretion of mucus; the digestive power is arrested; pain and fulness are felt; and loss of appetite (anorexia) and nausea are complained of. All these symptoms will call for relief by treatment.