THE NATURE OF THE ACID IN THE GASTRIC JUICE. 23 may, indeed, be supposed that when lactic acid has been present it may have been produced by the decomposition of the food; but this is evidently not always the case, for it has been detected in examples of gastric fistulæ, in which pure gastric juice has been extracted from the stomach after irritation had been excited by the swallowing of insoluble substances. The nature of the free acid seems to vary at different periods in the same person; thus, in a patient affected with gastric fistula under the care of Dr. Grünewaldt, at one time no hydrochloric acid could be found; whilst at another, when a free secretion had been excited by the swallowing of dry peas, hydrochloric acid was discovered, without any admixture of lactic acid.1 In dogs, Bidder and Schmidt found free hydrochloric acid in the gastric juice in eighteen experiments; in sheep hydrochloric acid was also present, but it was usually mixed with some lactic acid. The only way, I think, in which the conflicting statements of chemists upon this point can be reconciled, is to suppose that the lactic, butyric, and other acids may be present from the decomposition of par. ticles of food, which have been retained in the stomach; and also that the gastric juice may contain a certain proportion of any acid which may be present in salts admitting of ready decomposition, and with which the blood is charged at the time of digestion. The probability of the latter supposition will be better appreciated, when we remember that the mucous membrane of the stomach possesses the power of separating 1 Chambers on Digestion, p. 92. from the blood many abnormal materials with which that fluid may be contaminated. It has been found by experiment, that either dilute hydrochloric or lactic acid will form an artificial gastric juice, when joined with the mucous membrane of the stomach; but that the other mineral and vegetable acids fail to transform albumen into peptone. The presence of a free acid is, however, indispensable; for the solution of albumen is arrested if an alkali be added in excess. It is, no doubt, chiefly in this way that the presence of bile or alkaline mucus, or an excessive secretion of saliva, acts injuriously on the digestive process. The antiseptic properties of the gastric juice seem also to depend on the acid it contains; for, when it is neutralized by alkalies, or when saliva is mixed with it, decomposition takes place. The addition of water to gastric juice which has been already saturated with a peptone enables it to transform a further quantity of albumen; and, in like manner, a fresh supply of acid restores, to some extent, its digestive powers. Hydrochloric and lactic acids alone are not able to transform albumen into peptone. To enable them to do this, they must be mixed with some of the characteristic secretion of the stomach, which is named "pepsin." Pepsin is easily soluble in water, and may be kept for some time in the dry state without loss of its properties. It coagulates a solution of casein; but, without the addition of a free acid, it does not dissolve albumen. It is precipitated from its solution by bichloride of mercury, protochloride of tin, alcohol and tannic acid, and, in an imperfect manner, by neutral acetate of lead. THE AMOUNT OF PEPSIN SECRETED. 25 The amount of pepsin secreted seems to vary with the general health of the patient. In Dr. Grünewaldt's case, the gastric juice contained 43.4 parts in 1000 of solid matter, and 36.6 of this was pepsin, whilst the patient was well fed and under the observation of the physiologists; but "a great change was made by a return to the spare diet of an Esthonian cottage." Dr. Schröder's analyses were made four months after Dr. Grünewaldt's and when the patient had been at home some time; and then, instead of 43, only 5 parts of solid matter, and in place of 36, 3 of ferment appeared. In my own experiments, I have found that in some diseases—as in typhoid fever and in certain forms of cancer-the amount of pepsin contained in the mucous membrane of the stomach was exceedingly small; although, to the most minute examination, the tubes and cells presented a normal appearance. On the other hand, the greatest amount of pepsin was found in the stomachs of those who had been killed by accidents, or who had died of diseases which had produced but little effect on the general health. As it has been thus proved that the characteristic secretion of the stomach may be very small in amount, even where the structure appears to be normal, it seemed to me that it might be useful to ascertain the amount of pepsin contained in the gastric mucous membranes of persons dying from various diseases. The following plan was therefore adopted in a large number of cases. The stomach was emptied of its contents and placed in strong spirits of wine for a 1 Chambers on Digestion, p. 95. from the blood many abnormal materials with which that fluid may be contaminated. It has been found by experiment, that either dilute hydrochloric or lactic acid will form an artificial gastric juice, when joined with the mucous membrane of the stomach; but that the other mineral and vegetable acids fail to transform albumen into peptone. The presence of a free acid is, however, indispensable; for the solution of albumen is arrested if an alkali be added in excess. It is, no doubt, chiefly in this way that the presence of bile or alkaline mucus, or an excessive secretion of saliva, acts injuriously on the digestive process. The antiseptic properties of the gastric juice seem also to depend on the acid it contains; for, when it is neutralized by alkalies, or when saliva is mixed with it, decomposition takes place. The addition of water to gastric juice which has been already saturated with a peptone enables it to transform a further quantity of albumen; and, in like manner, a fresh supply of acid restores, to some extent, its digestive powers. Hydrochloric and lactic acids alone are not able to transform albumen into peptone. To enable them to do this, they must be mixed with some of the characteristic secretion of the stomach, which is named "pepsin." Pepsin is easily soluble in water, and may be kept for some time in the dry state without loss of its properties. It coagulates a solution of casein; but, without the addition of a free acid, it does not dissolve albumen. It is precipitated from its solution by bichloride of mercury, protochloride of tin, alcohol and tannic acid, and, in an imperfect manner, by neutral acetate of lead. THE AMOUNT OF PEPSIN SECRETED. 25 The amount of pepsin secreted seems to vary with the general health of the patient. In Dr. Grünewaldt's case, the gastric juice contained 43.4 parts in 1000 of solid matter, and 36.6 of this was pepsin, whilst the patient was well fed and under the observation of the physiologists; but "a great change was made by a return to the spare diet of an Esthonian cottage." Dr. Schröder's analyses were made four months after Dr. Grünewaldt's and when the patient had been at home some time; and then, instead of 43, only 5 parts of solid matter, and in place of 36, 3 of ferment appeared. In my own experiments, I have found that in some diseases—as in typhoid fever and in certain forms of cancer-the amount of pepsin contained in the mucous membrane of the stomach was exceedingly small; although, to the most minute examination, the tubes and cells presented a normal appearance. On the other hand, the greatest amount of pepsin was found in the stomachs of those who had been killed by accidents, or who had died of diseases which had produced but little effect on the general health. As it has been thus proved that the characteristic secretion of the stomach may be very small in amount, even where the structure appears to be normal, it seemed to me that it might be useful to ascertain the amount of pepsin contained in the gastric mucous membranes of persons dying from various diseases. The following plan was therefore adopted in a large number of cases. The stomach was emptied of its contents and placed in strong spirits of wine for a 1 Chambers on Digestion, p. 95. |