144. Composition of the Bile. the liver in part join the thoracic duct in the abdomen, in part, perforate the diaphragm, and ascend in the anterior cavity of the mediastinum. The bile is the secretion of the liver; the gall-bladder appears intended as a reservoir in which the bile is retained when not needed in the small intestine: the bile is supposed to become inspissated during its stay in the gallbladder through the absorption of its aqueous parts. The bile is sometimes green, sometimes of a yellowish brown, sometimes nearly colourless. Its taste is not very bitter. It is seldom completely liquid, but usually contains some yellow matter suspended in it. When evaporated to dryness, it leaves a brown matter amounting to about of the original weighta. The following are the constituents which Berzelius found in human bile. It appears that the secretion of bile may take place from arterial blood. Mr. Abernethy mentions having examined the body of a female infant, which measured two feet in length, and seemed about ten months old. The muscles of the child were large and firm, a Thomson's Chemistry, vol. iv. p. 513. Bile formed from Arterial and from Venous Blood. 145 and covered by a considerable quantity of healthy fat; and the appearance of the body strongly implied that the child had, when living, possessed much vigour of constitution. The liver was of the ordinary size, but had not the usual inclination to the right side of the body; it was situated in the middle of the upper part of the abdomen, and nearly an equal portion of the gland extended into either hypochondrium. The gall-bladder lay collapsed in its usual situation: it was of a natural structure, but rather smaller than common. It contained about a tea-spoonful of bile, in colour resembling the bile of children, being of a deep yellow; it also tasted like bile: it was bitter, but not so acridly or nauseously bitter as common bile. But in this infant the vena portæ terminated in the inferior cava, and the entire supply of blood to the liver was derived through an hepatic artery larger than common. On the other hand, the recent experiments of M. Simon upon pigeons have shown that when the hepatic artery is tied, the secretion of bile continues; but that if the veins of the porta and the hepatic canals be tied, no trace of bile is subsequently found in the liver: several pigeons survived the latter operation for six-and-thirty hours. In these animals it therefore appears that the secretion of bile takes place from venous blood. M. Simon observed that when the hepatic ducts alone were tied, the liver became choked up and filled with globules of a green tint; and that this colour was dif fused over the whole surface of the organ, and affected the adjoining parts: it is extremely remarkable that in e Phil. Trans. vol. lxxxiii. p. 61. L 146 Of Esophageal Deglutition. from ten to twenty hours after this experiment, the animals discharged by the anus matter absolutely green, and of the colour of the bile, with which the liver was overloaded;—and it seems not unreasonable to suppose that this appearance resulted from a vicarious secretion from the kidneys f. Perhaps we are bound to attribute the secretion of bile in human beings both to the artery and to the vein : that the venous blood returned from the bowels will serve, we may presume from the experiments narrated; and to employ it as far as it will go, upon this object, is consistent with the wise œconomy of Nature. SECTION 3. Of the Formation of Chyme. The progress of the food along the oesophagus is attended with sensation: it appears to be slow but uninterrupted, unless the solid part of the food be swallowed in morsels too large or hurriedly, when a draught of liquid is required to overcome the painful sense of obstruction which arises, and to facilitate the passage of the aliment towards the stomach by lubricating the surface of the canal. The fibres of the upper part of the œsophagus become relaxed as soon as the food has passed; but those belonging to the lower third of the tube remain firmly contracted for several seconds after its contents are expelled. M. Hallé observed in a woman afflicted by a malady which permitted the interior of the stomach to f Edinburgh Journal of Medical Science, No. I. p. 229. Accumulation of Food in the Stomach. 147 be seen, that at each entrance of food into the stomach the inner membranes were partially everted, so as to form a circular fold at the margin of the cardia. The sensations excited upon the oesophagus by pressure, laceration, and differences of temperature, exactly resemble those of the skin on similar occasions. This mode of sensibility appears to terminate at the cardia. The stomach seems to have no sensation excited by the contact of the food, unless it be the very obscure sensation of cold, which is referred to the epigastrium upon swallowing liquids at a low temperature. The stomach easily dilates towards the cardiac extremity. At one-third of its length from the pylorus, a remarkable contraction takes place upon the commencement of digestion, which divides the organ temporarily into two chambers. As the food accumulates within the cardiac portion, the stomach becomes prominent in the epigastrium, the abdomen is distended, the diaphragm cannot descend as readily as before, the inspirations are shorter and more frequent, the exertion of the voice becomes a greater effort, the neighbouring viscera are compressed, and the tendency to evacuate their contents is increased. To prevent the reflux of food along the œsophagus under these circumstances, its muscular fibres are observed to fall into frequent contractions, which for the most part take place at the periods of inspiration, when the pressure upon the abdomen is the greatest. The food collected in the great end of the stomach is exposed to the influence of varying pressure, of the partial contact of a living surface, and of the secretions of the stomach and fauces at a temperature of 97° or 98°. Under these circumstances the food appears gradually 148 Production of Chyme. to dissolve into a thick fluid, termed chyme, which is described as an uniform greyish pulp, more or less viscid, sweetish, acidulated, but varying in its qualities with the nature of the food from which it has been formed. Mr. Brodie mentions that in the stomach of a cat the lean or muscular part of animal food is converted into a brown fluid of the consistence of thin cream: while milk is first separated into its two constituent parts of coagulum and whey, the former of which is afterwards redissolved, and the whole converted into a fluid substance, with very minute portions of coagulum floating in it. Dr. Prout describes the chyme of a dog fed on vegetable food (principally bread) as composed of a semifluid opake yellowish white part, containing another portion of similar colour, but of firmer consistencé mixed with it. It showed no traces of a free acid or alkali, but coagulated milk completely, when assisted by a gentle heat. The chyme of a dog fed upon animal food was found by Dr. Prout to be more thick and viscid than the preceding, and its colour more inclining to red. It showed no traces of a free acid or alkali, nor did it coagulate milk, even when assisted by the most favourable circumstances. But these specimens of chyme were taken from the duodenum, and already impregnated with bile". The outer portion of a mass of food lying in the stomach is found to be the first converted into chyme: the chyme is observed gradually to accumulate at the pyloric portion of the organ. Dr. Wilson Philip mentions that when fresh food is taken into the stomach during digestion, "Quarterly Journal, No. xxviii. p. 342. |