to its place after the efforts have ceased. Astruc maintained, that the abdominal muscles had nothing to do with the act of defecation, which gave occasion to the jocose remark of Pitcairn,'-"Mihi videtur Astruccium nunquam cacasse alioquin sensisset musculos abdominis et se contrahere et alia exprimere posse.' Whilst straining is effected by the diaphragm and abdominal muscles, the longitudinal muscular fibres of the rectum contract, so as to shorten the intestine, and, consequently, the space over which the fæces have to pass. At the same time, the circular fibres contract from above to below, so as to propel the excrement downwards, and to cause the mucous membrane to extrude, and form a ring or bourrelet, like that which occurs at the cardiac orifice of the stomach, when the food is passing from the oesophagus into that organ. If this extrusion occurs to a great extent, it constitutes the disease called prolapsus ani. Dr. O'Beirne, of Ireland, guided by the following facts and arguments; that great irritation would be produced in the sphincter ani, and bladder, if the fæces descended readily into the rectum;-that the difficulty experienced in throwing up an injection is inconsistent with the idea of the gut being open, and proves that it is firmly contracted and closed; that when the surgeon has occasion to pass his finger up the rectum, he rarely encounters either solid or fluid fæces;-that the two sphincter muscles of the anus are weakened in certain diseases, and divided in operations, and yet it rarely happens, that the power of retaining the fæces is destroyed;-that on passing a stomach-tube to the height of half an inch up the rectum, in a number of healthy persons, it was found, that nothing escaped, and that the tube could be moved about freely in a space, which, on introducing the finger, was ascertained to be the pouch of the rectum; but that from the highest part of the pouch to the upper extremity of the gut-generally a distance of from six or seven to eight inches-it could not be passed upwards without meeting with considerable resistance, and without using a degree of force to mechanically dilate the intestine, which was plainly felt to be so contracted as to leave no cavity for this extent;that when the instrument reached, in this way, the highest point of the rectum, the resistance to its passage upward was felt to be sensibly increased, until, at length, by using a proportionate degree of pressure, it passed rapidly forward, as if through a ring, into a space in which its extremity could be moved with great freedom, and as instantly a rush of flatus, of fluid fæces, or of both, took place through the tube;-and that in every instance, where the tube presented the least appearance of fæces after being removed, this appearance was confined to that portion which had entered the sigmoid flexure:-guided by these and other facts, Dr. O'Beirne concluded, that in the healthy and natural state, all the part of the rectum above its pouch is at all times, with the single exception of a few minutes previous to the evacuation of the bowels, firmly contracted, and perfectly empty, at the 1 Opuscula medica (Lector) Roterodam, 1714. 2 New Views of the Process of Defecation, &c., Dublin, 1833; reprinted in this country, Washington, 1834. same time that the pouch itself, as well as the sigmoid flexure of the colon, is always more or less open, and pervious,-and that the sphincter ani muscles are but subsidiary agents in retaining the fæces. When the fæces are firm, considerable muscular effort is necessary to expel them; but when they are of a softer consistence, the contraction of the rectum is sufficient. The sphincters-as elsewhere shown-afford examples of reflex action. After sensation and volition are suspended, they contract under direct irritation. Yet, like the respiratory muscles, they are of a mixed character,-partly voluntary and partly involuntary. They are involuntary, but capable of being aided or impeded by a voluntary effort. The state of gentle contraction, in which they constantly are, is evidently dependent upon their connexion with the spinal cord; for the experiments of Dr. Marshall Hall have exhibited, that it ceases, when the connexion is destroyed. Air, contained in the intestinal canal, readily moves about from place to place, and speedily reaches the rectum by the peristaltic action alone. Its expulsion, however, is commonly accomplished by the aid of the abdominal muscles; when it issues with noise. If discharged by the contraction of the rectum alone, it is generally in silence. Children are extremely subject to flatulence; in the adult it is not so common. Certain kinds of diet favour its production more than others, especially in those of weak digestive powers, of which condition its undue evolution is generally an indication. The leguminous and succulent vegetables in general belong to this class. Where digestion is tardily accomplished, they give occasion to the copious disengagement of gas. Too often, however, the disgusting habit of constantly discharging air streperously from the bowels is encouraged, rather than repressed; and there are persons, who are capable of effecting the act almost as frequently as they attempt it. The noise, made by the air, as it passes backwards and forwards in the intestinal canal, constitutes the affection called borborygmus. So much for the digestion of solid food. In so delicate and complicated an apparatus, it would seem, that mischief ought more frequently to result from the various heterogeneous substances that are received into the digestive tube. Its resistance, however, to morbific agencies is astonishing. In the Museum of the Boston Society for Medical Improvement' an open penknife is preserved, which was swallowed by a child between three and four years of age, and passed from the bowels after the expiration of fifty-one hours; the child, in the meantime, playing about as usual, and not seeming to suffer. The story of the lunatic, under the care of Dr. Fox of Bristol, who swallowed "some inches" of a poker, which came away without any suffering, is regarded as authentic; and there is no question in regard to the authenticity of the case of the sailor recorded by Dr. Marcet,' who swallowed a num J. B. S. Jackson, A Descriptive Catalogue of the Anatomical Museum of the Boston Society for Medical Improvement, p. 158, Boston, 1847. Southey, The Doctor, iv. 297, Lond., 1837. Medico-Chirurgical Transactions, xii. 52, Lond., 1822. ber of clasp knives with impunity, but ultimately fell a victim to his idle temerity,—having swallowed, in the whole, thirty-seven! 5. DIGESTION OF LIQUIDS. In inquiring into the digestion of liquids, we shall follow the same order as that observed in considering the digestion of solids; but as many of the acts are accomplished in the same manner, it will not be necessary to dwell upon them. Thirst or the desire for drink is an internal sensation; in its essence resembling that of hunger, although not referred to the same organs. It arises from the necessities of the system; from the constant drain of the fluid portions of the blood; and is instinctive or essentially allied to organization.' The sensation differs in different persons, and is rarely alike in the same. Usually, it consists of a feeling of dryness, constriction, and heat in the back part of the mouth, pharynx, oesophagus, and occasionally in the stomach; and, if prolonged, redness and tumefaction of the parts supervene, with a clammy condition of the mucous follicular-and diminution and viscidity of the salivary-secretions. These phenomena are described as being accompanied by restlessness, general heat, injected eyes, disturbed mind, acceleration of the circulation, and short breathing, the mouth being frequently and largely open, so as to admit the air to come in contact with the irritated parts, and thus afford momentary relief. Thirst is a very common symptom of febrile and inflammatory diseases, in which fluid-especially cold fluid-is desired in consequence of the local relief it affords to the parched and heated membrane of the alimentary canal. It is also developed by extraneous circumstances, as in summer, when the body sustains considerable loss of fluid; as well as in those diseases-dropsy, diabetes, &c.-which produce the same effect. There are many other circumstances, however, that excite it;-long speaking or singing; certain kinds of diet as the saline and spicy, and especially the habit, acquired by some, of drinking frequently. Whilst individuals, thus circumstanced, may need several gallons a day to satisfy their wants;-others, who have, by resistance, acquired the habit of using very little liquid, may be enjoying health, and not experiencing the slightest inconvenience from the privation of liquid; so completely are we, as regards the character and quantity of our aliment, the creatures of habit. This privation, it is obvious, cannot be absolute or pushed beyond a certain extent. There must always be fluid enough taken to administer to the necessities of the system. As in the production of all sensations, three acts are required for accomplishing that of thirst;--impression, conduction, and perception. The last, as in every similar case, is effected by the brain; and the second by the nerves passing between the part impressed and that organ. The act of impression-its seat and cause-will alone arrest our attention, and it will be found that we are still less instructed on these points than on the physiology of hunger. Even with regard to the seat of the impression, we are in a state of uncertainty. It appears to be chiefly in the back part of the mouth and fauces; but whether 1 J. Béclard, Traité Élémentaire de Physiologie, p. 28, Paris, 1855. primarily there, or experienced there by sympathy with the condition of the stomach, is by no means clear. The latter opinion, however, appears the more probable. In a remarkable case, published by Dr. Gairdner of Edinburgh, it was found impracticable to allay thirst by merely supplying the mouth, tongue, and fauces with fluid. A man had cut through the oesophagus. An insatiable thirst arose; several pailfuls of water were swallowed daily, and discharged through the wound without removing the desire for drink; but on injecting water, mixed with a little spirit, into the stomach, it was soon quenched. That the sensation is greatly dependent upon the quantity of fluid circulating in the vessels is shown by the fact, mentioned by M. Dupuytren, that he succeeded in allaying the thirst of animals, by injecting milk, whey, water or other fluids into the veins; and M. Orfila states, that, in his toxicological experiments, he frequently allayed in this way the excessive thirst of animals, to which he had administered poison; and which were incapable of drinking, owing to the oesophagus having been tied. He found, also, in his experiments, that the blood of animals was more and more deprived of its watery portions as the abstinence from liquids was more prolonged.' Like all other sensations, that of thirst arises from an inappreciable modification of the nerves of the organ: hence, all the hypotheses proposed to accour for it have been mere fantasies undeserving of enumeration. The prehension of liquids differs somewhat from that of solids. The fluid may be simply poured into the mouth, or a vacuum may be formed in it: the pressure of the atmosphere then forces it in. When we drink from a vessel, the mouth is applied to the surface of the fluid; the chest is then dilated, so as to diminish the pressure of the atmosphere on the portion of the surface of the liquid intercepted by the lips; and the atmospheric pressure on the surface of the fluid in the vessel forces it into the mouth, to replace the air that has been drawn. from the mouth by the dilatation of the thorax. In sucking, the mouth may be compared to an ordinary syringe; the nozzle of which is represented by the lips; the body by the cheeks, palate, &c., and the piston by the tongue. To put this in action, the lips are accurately adjusted around the body from which the liquid has to be extracted. The tongue is likewise applied, contracts, and is carried backwards; so that an approach to a vacuum is formed between its upper surface and the palate. The fluid, no longer compressed equally by the atmosphere, is displaced, and enters the mouth. As neither mastication nor insalivation is required in the case of liquids, they do not remain long in the mouth, unless their temperature is too elevated to admit of their being passed down into the stomach immediately, or they are of so luscious a character, that their prolonged application to the organ of taste affords pleasure. Their deglutition is effected by the same mechanism as that of solids; and, as they yield readily to the slightest pressure, with less difficulty. Their accumulation in the stomach takes place in much the same manner. They arrive by successive mouthfuls; and, as they collect, the thirst disappears Adelon, Physiologie de l'Homme, 2de édit., ii. 525, Paris, 1829. with all its local and general attendants. If, however, the organ be over-distended a disposition to vomiting is induced. The changes, which liquids undergo in the stomach, are of different kinds. All acquire the temperature of that viscus, and become mixed with the secretions from its internal surface, as well as from that of the supra-diaphragmatic portion of the digestive tube. Some, however, undergo the operation of chymification; others not. To the latter class belong, water, weak alcoholic drinks, the vegetable acids, &c. Water experiences the admixture already mentioned; becomes turbid, and gradually disappears, without undergoing any transformation. Part passes into the small intestine; the other is directly absorbed. When any strong alcoholic liquor is taken, the effect is different. Its stimulation causes the stomach to contract, and augments the secretion from the mucous membrane; whilst, at the same time, it coagu lates all the albuminous portions; mixes with the watery part of the mucous and salivary fluids, and rapidly disappears by absorption; hence, the speedy supervention of inebriety, or death, after a large quantity of alcohol has been taken into the stomach. The substances, that have been coagulated by the action of the alcohol, are afterwards digested like solid food. We can thus understand the good effects of a small quantity of alcohol, taken after a substance difficult of digestion,—a custom which has existed from high antiquity, and has physiology in its favour. It is, in such cases,-to use the language of the eccentric Kitchener,'-a good "peristaltic persuader." Oil remains longer in the stomach than any other liquid, experiences little change there, but passes into the small intestine, where it forms an emulsion and enters the veins and chyliferous vessels. Milk, as is well known, coagulates in the stomach soon after it is swallowed, after which the clot is digested, and the whey absorbed. Yet the existence of coagula in the stomach is constantly regarded by the unprofessional as a pathological condition! Where the liquid, aqueous or spirituous, holds in suspension the immediate principles of animals or vegetables, as gelatin, albumen, osmazome, sugar, gum, fecula, colouring matter, &c., there is reason to believe that they enter immediately into the veins of the stomach and small intestine, having become modified and rendered fit for assimilation by admixture with the gastric and intestinal secretions. The salts, united with these fluids, are taken up along with them. Red wine, according to M. Magendie, first becomes turbid by admixture with the juices formed in, or carried into, the stomach; the albumen of these fluids speedily undergoes coagulation, and becomes flocculent; and, subsequently, its colouring matter-entangled, perhaps, with the mucus and albumen-is deposited on the mucous membrane of the stomach. The aqueous and alcoholic portions soon disappear. Liquids reach the small intestine in two forms;-in the state of chyme; and in their unaltered condition. In the former case, they proceed like the chyme obtained from solid food. In the latter, they ' Directions for Invigorating and Prolonging Life; or the Invalid's Oracle, &c., Amer. edit., from the 6th London, by T. S. Barrett, New York, 1831. 2 Précis, &c., ii. 143. |