83. After the chyme has passed into the duodenum, it becomes mixed and incorporated with the peculiar fluid secreted by that intestine; it still, however, preserves its colour, its semi-fluid consistence, its sharp odour, and its slightly acid savour, until it reaches the sacculated angle, where it meets with the biliary and pancreatic fluids, with which it mixes, and undergoes an important chemical change, which has been very accurately examined by M. Majendie; and as the re-suits of his inquiry are capable of throwing some light upon the subject, I shall offer a summary view of them. As soon as the chyme mingles with the chy-lopoietic fluids, it assumes a yellow colour and a bitter taste, and its sharp odour is diminished; but those changes, as well as the phenomena which accompany them, are variable, and appear to be influenced by the quality of the food. If the chyme proceed from animal or vegetable matters containing fat or oil, irregular filaments, sometimes flat, and at other times rounded, are seen to form here and there on its surface, and to attach themselves quickly to the valvules conniventes. They appear to consist of crude chyle.

This matter, however, was not observed when the aliment did not contain fat: in the latter case, the product appeared as a greyish layer, more or less thick, adhering to the mucous membrane, and might possibly contain only the elements of chyle. This change, whatever may be its chemical nature, is evidently produced by the action of the biliary and pancreatic liquids, aided by the agitation which the substances undergo by the motions of the duodenum itself, as well as by that communicated to it from the colon, to which it is attached.

84. Various opinions have existed, with regard to the use of the bile: some physiologists have considered it as merely excrementitious, and with this opinion the general mass of mankind would appear to coincide; for there is scarcely a patient who does not complain of being tormented with bile, while the shop of the druggist groans with the weight of pills which are calculated to expel this fearful enemy from the system. The situation alone of the liver, connected as it is, in every instance, with the upper part of the alimentary canal, would be sufficient to repel such an idea. Others have imagined, that it is a natural and habitual stimulus to the intestines, keeping up their energy and peristaltic motion. It cannot be denied that this is one of its secondary uses; it likewise, from its saponaceous and soluble qualities, diminishes the adhesive nature of the faeces, and, by smoothing their surfaces, promotes their evacuation; but its first and most important use is to change the nutritive part of the chyme into a new and more highly animalized product, termed chyle 1 and to separate from it the useless and excre-mentitious part.

That such is the truth, is at once proved by the fact, that chylification takes place just at the part where the bile flows into the intestine: nothing like chyle is ever found in the stomach; and Dr. Prout, whose able researches in animal chemistry are well known, has ascertained that albumen, which is the characteristic part of chyle, is never to be discovered in herbivorous animals higher than the pylorus. The question is, moreover, set at rest by the experimental inquiries of Sir Benjamin Brodie. He tied a ligature round a common duct of a cat, so as completely to prevent the entrance of the bile into the intestine; he then noted the effects produced in the digestion of the food which the animal had swallowed, either immediately before, or after the operation. The experiment was repeated several times, and the results were uniform. The production of chyme took place as usual, but the conversion of chyme into chyle was invariably and completely interrupted. Not the smallest trace of this latter fluid was discoverable, either in the intestines or in the lacteals.

The former contained a semi-fluid substance, resembling the chyme found in the stomach, with this difference, that it became of a thicker consistence, in proportion as it was at a greater distance from the stomach, and that, as it approached the termination of the ilium, the fluid part of it had altogether disappeared, and there remained only a solid substance, differing in appearance from ordinary faeces. The lacteals contained a transparent fluid, which probably consisted partly of lymph, partly of the more fluid parts of the chyme which had been absorbed. These experiments, then, clearly demonstrate, that the office of the bile is to change the nutritive part of the chyme into chyle, and to separate from it the excre-mentitious matter. How, then, it may be asked, does it happen, that persons live to a considerable period, in whom the flow of bile into the duodenum is interrupted? The truth is, that the obstruction of the duct by disease is seldom so complete as to prevent the passage of bile altogether, and the white appearance of the faeces may prove the deficiency, or morbid condition, but not the total absence of bile.

To ascertain how far this supposition might be supported by experiment, I poured some dilute muriatic acid upon a portion of faeces that was perfectly white, when a green colour was immediately produced, which could not have happened without the presence of bile.

1 With respect to the terms chyme and chyle, Dr. Bostock makes the following observation: - "It does not appear that there is anything in their etymology which would lead to the distinction thus admitted, nor was it recognised by the old authors, nor even by some of those of the last century, who appear to have used the words indifferently, or to have considered them as synonymous. The distinction between chyme and chyle is not recognised by Boer-haave; he appears, indeed, not to contemplate any essential difference between the contents of the stomach and the duodenum, except what depended upon the mixture of bile and pancreatic juice with the latter. I have not been able to ascertain who it was that first assigned to the words their present signification." - Bos-tock's Physiology.