In considering the diseases of the stomach, it is necessary to bear in mind certain points in regard to the structure and functions of the organ. The innumerable glands which exist in the mucous membrane are engaged in the formation of the Gastric juice for the purposes of digestion. The diseases of the stomach very readily interfere with the function of these glands, so that the secretion of gastric juice is insufficient in quantity or deteriorated in quality. In, that case the Food is apt to lie in the stomach undigested, and it very commonly undergoes various forms of Decomposition. The products of decomposition acting on the mucous membrane still further interfere with the process of secretion, and by their irritative action keep up or induce a condition of catarrh of the stomach. Gases also develop in the process of decomposition, and these, by distending the organ, interfere with its proper peristaltic movements, and so hinder the passage of the food through the pylorus.
But it is not merely local diseases, such as inflammations and tumours, which interfere with the secretion of the gastric juice. Changes characterized by Cloudy swelling and Fatty degeneration are met with in the glandular epithelium in numerous infective diseases, small-pox, typhus, septicaemia, as also in poisoning with phosphorus, etc. In these cases the secretion of the gastric juice may be almost at a standstill, and if food be introduced it is apt to lie in the stomach; by its mere presence, and by the action of the products of decomposition, it may produce still further structural changes.
The forms of decomposition which the food undergoes when it lies undigested in the stomach are various, but the chief are those characterized by the development of Acetic, Lactic, and Butyric acids. The agents in these changes are microbes which are introduced in abundance with the food and propagate in the stomach, unless their multiplication is hindered by the action of the gastric juice. In the contents of the stomach, when at any time they are discharged during life, swarms of bacteria are found, and in addition there are nearly always proliferating spores of fungi and sometimes large numbers of sarcinse.
It has been mentioned that the products of decomposition irritate the mucous membrane, but, in addition to that, microbes have been found in some cases to enter the glands and mucous membrane. In some of the cases the action of such microbes has produced little Pustules in the mucous membrane, or even larger prominences with necrosis and ulceration. It may be inferred that it is microbes of a special kind or in a peculiar state of activity which thus penetrate into the mucous membrane. Stagnation of the food in the stomach and its decomposition will occur still more when, by stricture of the pylorus, there is a Mechanical obstacle to the passage from the stomach.
Besides the mere local effects induced by the products of decomposition, it is to be remembered that the mucous membrane of the stomach is actively engaged in Absorption, and that these products may to some extent be taken into the blood. It is probable that the headache and other nervous symptoms occurring in dyspepsia are in great measure due to the existence in the blood of small quantities of these poisonous agents and their action on the nervous system.
When the food remains in the stomach and accumulates there, it is usually got rid of after a time by Vomiting. This action is produced by irritation of a centre in the medulla oblongata, and the muscles employed are mainly those used in respiration, but in different combinations. The centre may be irritated directly, as by introducing apomorphia or tartar emetic into the blood, or by disease of the brain itself. But in the case we are considering it is irritated by reflex stimulation, the stimulation taking origin in centripetal fibres in the stomach itself. The occurrence of vomiting is dependent on the nature and amount of the irritation applied and on the sensitiveness of the centre in the individual.
After death, any remains of food lying in the stomach are apt to decompose rapidly, especially as the gastric juice in most cases is not secreted in the normal way up to the period of death, and so the decomposition is not interfered with. The decomposing juices therefore act readily on the mucous membrane, and the decomposition may even extend to the latter. The principal changes produced are Alterations in colour, resulting from chemical changes in the colouring matter of the blood. This may become diffused out of the blood-vessels and stain the mucous membrane of a generally red hue, the colour being specially pronounced in the neighbourhood of the larger vessels. There is often a greenish colour developed by the decomposition of the blood. Lastly, the colour may be almost black or slaty, but in many cases this deep colour is not altogether post-mortem, depending in part on a true pigmentation from chronic catarrh of the mucous membrane.
Softening of the stomach or Gastromalacia is also a post-mortem change. It is really a digestion of the coats of the stomach by the gastric juice. As a rule, in persons near death, the gastric juice is not secreted normally, but if the person die while the secretion of gastric juice is still active, then the latter may, by a process of Digestion, act on the coats of the stomach. This condition occurs mostly in persons who die suddenly, especially if the body is kept in a warm place, and it is more frequent in children than in adults. In the slightest degree, the mucous membrane alone is softened, and it can be removed by the linger as a soft paste from the surface of the muscular coat. Penetrating deeper, the muscular coat and even the serous coat may be half liquefied, so that on handling the stomach it may be perforated. The stomach may even Rupture in the body, and the contents pass outwards, producing softening in neighbouring parts. In some cases the diaphragm has been softened in this way, and the stomach contents have passed partly into the pleural cavity.
These various changes occur in those parts of the stomach where the contents have been lying after death. This is generally the neighbourhood of the fundus. As the contents are usually fluid, it is often seen that the changes stop short at a definite level and the unaltered mucous membrane is abruptly demarcated from the altered part. The pyloric portion of the stomach, as it usually lies highest, is-least frequently affected, and this is important, as that part of the stomach is the most frequent seat of disease.
It must be borne in mind that the pathological changes met with in the stomach are very often obscured by the occurrence of these post-mortem changes.
Leube, in Ziemssen's Encycl., vii., 1877; Kussmaul, D. Arch. f. klin. Med., vi.; Brunton, Disorders of digestion, 1886. Digestion of stomach - Hunter, Phil, trans., 1772, and Works by Palmer, iv., 116; Burns, Med. and Surg. Jour., 1810; Bamberger, Krankb. d. chylop. Syst., 1855; Virchow, Wurzb. Verhandl., 1850; Reeves, Softening of stom. in children and adults, 1867.