property, when acidulated, of inducing decomposition and subsequent solution of the food; but it would appear, that no other mucus than that of the gastric mucous membrane, when acidulated, possesses it,' and, consequently, that there must be a peculiar substance, pepsin or gastric ferment, which may be regarded as a true digestive principle. This principle was not obtained by Schwann in a pure state; but M. Wasmann3 would appear to have succeeded better. A solution, containing only too part of pepsin and slightly acidulated, is said to dissolve the white of an egg in six or eight hours. It is not generally considered, however, to be a distinct substance-an immediate principle; but rather to be the product of an alteration of the nitrogenized matters of the parietes of the stomach.5 An artificial digestive fluid is sometimes made which resembles that of the human stomach, by macerating in water portions of fresh or dried mucous membrane of the stomach of a pig or other omnivorous animal, or of the fourth stomach of the calf, and adding to the infusion a few drops of chlorohydric acid, about 3.3 grains to half an ounce of the mixture according to Schwann. Portions of food placed in this fluid, and the mixture kept at a temperature of about 100°, are softened and changed, much in the same manner as they would be in the stomach." Even were the evidence adduced less positive in favour of the existence of some gastric secretion concerned in the digestive changes in that organ, the following phenomena would be overwhelming. Besides the fact of the most various and firm substances being reduced to chyme in the stomach, we find the secretions from its lining membrane possessing the power of coagulating albuminous fluids. It is upon the coagulating property of these secretions, that the method of making cheese is dependent. Rennet, employed for this purpose, is an infusion of the digestive stomach of the calf, which, on being added to milk, converts the albuminous portion into curd; and it is surprising how small a quantity is necessary to produce this effect. Messrs. Fordyce and Young, of Edinburgh, found that six or seven grains of the inner coat of a calf's stomach, infused in water, afforded a liquid, which coagulated more than one hundred ounces of milk,-that is, more than six thousand eight hundred and fifty-seven times its own weight; and yet its weight was probably but little diminished. The substance that possesses this property does not appear to be very soluble in water; for the inside of a calf's stomach, after having been steeped in water for six hours, and well washed, still furnishes a liquor or infusion, which coagulates milk. Liebig' has denied, that the fresh 1 Müller, Elements of Physiology, by Baly, pp. 518 and 542, London, 1838. • Müller and Schwann, in Müller's Archiv., Heft 1, 1836; and Müller, op. citat. Journ. de Pharmacie; and American Journal of Pharmacy, for Oct., 1840, p. 192. ♦ Graham's Elements of Chemistry, Amer. edit., p. 695, Philad., 1843, and Thomson's Animal Chemistry, p. 229, Edinb., 1843. Robin and Verdeil, Traité de Chimie Anatomique, &c., iii. 555, Paris, 1853; and Becquerel and Rodier, Traité de Chimie Pathologique, p. 470, Paris, 1853. Kirkes and Paget, Manual of Physiology, 2d Amer. edit., p. 173, Philad., 1853. 7 A Treatise on the Digestion of Food, p. 57, 2d edit., Lond., 1791. Thomson's System of Chemistry, 6th edit., iv. 596. • Animal Chemistry, Webster's Amer. edit., Cambridge, 1842. lining membrane of the stomach of the calf, digested in weak chlorohydric acid, gives to that fluid the power of dissolving boiled flesh or coagulated white of egg; but Dr. Pereira' affirms, that he has found, by experiment, that a digestive liquor can be prepared from the fresh undried stomach of a calf. This had, indeed, been shown on the best authority long ago. Mr. Hunter, for example, made numerous experiments upon the coagulating power of the secretions of the stomach, which show, that it is found in the stomachs of animals of very different classes. The lining of the fourth stomach of the calf is in common use, in a dried state, for the purpose mentioned above; and it has been proved, that every part of the membrane possesses the same property. Mr. Hunter found, by experiment, that the mucus of the fourth cavity of a slink calf, made into a solution with a small quantity of water, had the power of coagulating milk; but that found in the three first cavities possessed no such power. The former, even after it had been kept several days, and was beginning to be putrid, retained the property. The duodenum and jejunum, with their contents, likewise coagulated milk; but the process was so slow as to give rise to the suggestion, that it might have occurred independently of the intestines employed for the purpose. He found, that the inner membrane of the fourth cavity in the calf, when old enough to be killed for veal, had the same property. Portions of the cuticular, of the massy glandular part, and of the portion near the pylorus of the boar's stomach, being prepared as rennet, it was found, that no part had the effect of producing coagulation but that near the pylorus, where the gastric glands of the animal are especially conspicuous. The crop and gizzard of a cock were salted, dried, and afterwards steeped in water. The solution, thus obtained, was added to milk: the portion of the crop coagulated it in two hours; that of the gizzard in half an hour. The contents of a shark's stomach and duodenum coagulated it instantaneously. Pieces of the stomach were washed clean, and steeped in water for sixteen hours. The solution coagulated milk immediately. Pieces of the duodenum produced the same effect. When the milk was heated to 96°, the coagulation took place in half an hour; when cold, in an hour and a quarter. The stomachs of the salmon and thornback, made into rennet, coagulated milk in four or five hours. But those experiments of Mr. Hunter do not inform us of the particular secretions that are productive of the effect. They would, indeed, rather seem to show, that it is a general property of the whole internal membrane. To discover the exact seat of the secretion, and especially whether it be not in the gastric glands, Sir Everard Home2 selected those of the turkey; which, from their size, are better adapted for such an experiment than those of any other bird, except the ostrich. A young turkey was kept a day without food, and then killed. The gastric glands were carefully dissected separately from the lining of the cardiac cavity; cutting off the duct of each before it pierced the membrane, so that no part but the glands themselves were removed. 1 Treatise on Food and Diet, Amer. edit., p. 36, New York, 1843. 2 Lectures on Comparative Anatomy, i. 299, Lond., 1814, and iii. 134, Lond., 1823. Forty grains, by weight, of these glands were added to two ounces of new milk; and similar experiments were made with rennet; with the lining of the cardiac cavity of the turkey; and with the inner membrane of the fourth cavity of the calf's stomach. Coagulation and separation into curds and whey were first effected by the rennet. Next to this, and simultaneously, came the gastric glands, and the fresh stomach of the calf; and lastly, the cardiac membrane of the turkey. From these experiments, Sir Everard concluded, that the power of coagulation is in the secretion of the gastric glands; and that the power is communicated to other parts, by their becoming more or less impregnated with it. The marginal figure, copied from an engraving of the microscopic observations of Mr. Bauer, exhibits the gastric glands--as he regarded them--of the human oesophagus magnified fifteen times. These glands are in the lining of the lower part of the oesophagus; and have the appearance of infundibular cells, whose depth does not exceed the thickness of the membrane. This structure, although different from that of the gastric glands of birds, is a nearer approach to it than is to be met with in any part of the inner surface of the stomach or duodenum. It also resembles them, in the secretion. which it produces coagulating milk, whilst none Fig. 53. of the inspissated juices, Gastric Glands of the Esophagus magnified fifteen times. met with in these cavities, according to Sir Everard, affect milk in the same way. From these facts, he thinks, there can be no longer any doubt entertained, that the gastric glands have the same situation respecting the cavity of the stomach as in birds. No histologist, however, agrees with him in this location of the gastric glands. In some experiments, undertaken by M. J. F. Simon' with a view to determine, whether the stomach of the child possesses the same. properties of coagulating milk as that of the calf, he found that cow's milk was not coagulated by it, but that, when a quantity of the colostrum of the mother of a child, which died when five days old, was obtained, and a piece of calf's stomach was introduced into it, the milk coagulated. Another property, manifestly possessed by the secretion in question, is that of preventing putrefaction, or of obviating it in substances exposed to its action. Montègre and Thackrah' deny it this property, but there can be no doubt of its existence. Spallanzani, Fordyce, and Müller's Archiv., Heft 1, 1839, cited in Brit. and For. Med. Rev., Oct., 1839, p. 549. 2 Lectures on Digestion and Diet, p. 14, Lond., 1824. others, have ascertained, that in those animals which frequently take their food in a half putrid state, the first operation of the stomach is to disinfect, or remove the foetor from the aliment received into it. We have already alluded to many facts elucidative of this power. Helm of Vienna,' in the case of a female who had a fistulous opening in her stomach, observed, that substances which were swallowed in a state of acidity or putridity, soon lost those qualities in the stomach; and the same power of resisting and obviating putrefaction has been exhibited in experiments made out of the body. Nothing could be more unequivocal, as regards the possession of this property by the gastric fluid, than the experiments of Dr. Beaumont and the author,2 with the secretion obtained from the subject of his varied investigations. In the presence of the author's friend, N. P. Trist, Esq.-then consul of the United States at Havana,-the odour of putrid food was as speedily removed by it as by chlorinated soda employed at the same time on other portions. The explanation of this property, as well as that of coagulation, has been a stumbling-block to the chemical physiologist. "We can only say concerning it," says Dr. Bostock,3 "that it is a chemical operation, the nature of which, and the successive steps by which it is produced, we find it difficult to explain; at the same time, that we have very little, in the way of analogy, which can assist us in referring it to any more general principle, or to any of the established laws of chemical affinity." The cases of what are termed digestion of the stomach after death afford us, likewise, remarkable examples of the presence of some powerful agent in the stomach; as well as of the resistance to chemical action, offered by living organs. Powerful as the action of the gastric juice may be, in dissolving alimentary substances, it does not exert it upon the coats of the stomach during life. Being endowed with vitality, they effectually resist it. But when that viscus has lost its vitality, its parietes yield to the chemical power of the contained juices, and become softened, and, in part, destroyed. Mr. Hunter' found the lining membrane of the stomach destroyed, in several parts, in the body of a criminal, who, for some time before his execution, had been prevailed upon, in consideration of a sum of money, to abstain from food. Since Hunter's time, numerous examples have occurred, and been recorded by Messrs. Baillie, Allan Burns, Haviland, Grimaud, Pascalis, Cheeseman, J. B. Beck, Chaussier, Yelloly, Gardner, Treviranus, Gödecke, Jäger, Carswell, and others. The fact is of importance in medical jurisprudence; and, until a better acquaintance with the subject, would, doubtless, have been set down as strong corroborative evidence in cases 1 Rudolphi, Grundriss der Physiologie, 2er Band, 2te Abtheil., s. 114, Berlin, 1828. 2 See the author's Elements of Hygiene, p. 216, Philad., 1835. 3 Edit. citat., p. 571. Phil. Transact., lxii.; and Observations on certain parts of the Animal Economy, with notes by Prof. Owen, Amer. edit., p. 144, Philad., 1840. 5 Beck's Medical Jurisprudence, 6th edit., ii. 311, Albany, 1838; Carswell's Path. Anat., No. 5, Lond., 1833; and T. Wilkinson King, Guy's Hospital Reports, vii. 139, Lond., 1842; and a case communicated to the author by Dr. Thomas M. Flint, in which the stomach had separated from the œsophagus, recorded in Med. Examiner, p. 715, for December, 1848; also, Dr. George Budd, on the Organic Diseases and Functional Disorders of the Stomach, Amer. edit., p. 19, Philad., 1856. of suspected poisoning. It is now established that solution of the stomach may take place after death, without there being reason for supposing that any thing noxious had been swallowed. The experiments of Dr. Wilson Philip' and Sir Robert Carswell2 are corroborative of this physiological action of the gastric juice. On opening the abdomen of rabbits, that had been killed immediately after having eaten, and allowed to lie undisturbed for some time before examination, the former found the great end of the stomach soft, eaten through, and sometimes altogether consumed; the chyme being covered only by the peritoneal coat, or lying quite bare for the space of an inch and a half in diameter: and, in this last case, a part of the contiguous intestines was also destroyed; whilst the cabbage, which the animal had just taken, lay in the centre of the stomach unchanged, if we except the alteration that had taken place, in the external parts of the mass it had formed, in consequence of imbibing gastric fluid from the half-digested food in contact with it. Why the perforation takes place, without the food being digested, is thus explained by Dr. Philip. Soon after death, the motions of the stomach, which are constantly carrying on the most digested food towards the pylorus, cease. The food, that lies next to the surface of the stomach, thus becomes fully saturated with gastric fluid; neutralizes no more; and no new food being presented to the fluid it acts on the stomach itself, now deprived of life, and equally subjected to its action with other dead animal matter. It is extremely remarkable, however, that the gastric fluid of the rabbit, which, in its natural state, refuses animal food, should so completely digest the stomach, as not to leave a trace of the parts acted upon. Dr. Philip remarks, that he has never seen the stomach eaten through except at the larger end; but, in other parts, the external membrane has been injured. Mr. A. Burns, however, affirms, that in several instances he found the forepart of the stomach perforated about an inch from the pylorus, and midway between the smaller and larger curvatures. From all these facts, then, we are justified in concluding, that the food in the stomach is subjected to the action of secretions, which alter its properties, and are the principal agents in converting it into chyme. But many physiologists, whilst they admit, that the change effected in the stomach is of a chemical character, contend, that the nature of the action is unlike what takes place in any other chemical process, and is, therefore, necessarily organic and vital, and appertaining to vital chemistry. Such are the sentiments of Messrs. Fordyce, Broussais,' Chaussier, and Adelon," and others. Dr. Prout suggests, that the stomach must have, within certain limits, the power of organizing and vitalizing the different alimentary substances; so as to render them fit for being brought into more intimate union with a living body, than 1 Treatise on Indigestion, Lond., 1821. 2 Ibid. and Edinb. Med. and Surg. Journal, Oct.. 1830; and art. Perforation of the Hollow Viscera, in Cyclopædia of Practical Medicine, P. xvi. p. 272, Lond., 1833. Edinb. Med. and Surg. Journal, vi. 132. On the Digestion of Food, 2d edit., Lond., 1791. Traité de Physiologie, &c., translated by Drs. Bell and La Roche, p. 323. VOL. I.-11 |