lished an intestinal fistula below, from which they extracted the fluids which accumulated in the cavity of the gut. From the great abundance of the follicles of Lieberkühn, we should expect to find the intestinal juice secreted in large quantity. It appears, however, in point of fact, to be quite scanty, as the quantity collected in the above manner by experimenters has rarely been sufficient for a thorough examination of its properties. It seems to resemble very closely, in its physical characters, the secretion of the mucous follicles of the mouth. It is colorless and glassy in appearance, viscid and mucous in consistency, and has a distinct alkaline reaction. It has the property, when pure, as well as when mixed with other secretions, of rapidly converting starch into sugar, at the temperature of the living body.

PANCREATIC JUICE, AND THE DIGESTION OF FAT.

The only remaining ingredients of the food that require digestion are the oily matters. These are not affected, as we have already stated, by contact with the gastric juice; and examination shows, furthermore, that they are not digested in the stomach. So long as they remain in the cavity of this organ they are unchanged in their essential properties. They are merely melted by the warmth of the stomach, and set free by the solution of the vesicles, fibres, or capillary tubes in which they are contained, or among which they are entangled; and are still readily discernible by the eye, floating in larger or smaller drops on the surface of the semi-fluid alimentary mass. Very soon, however, after its entrance into the intestine, the oily portion of the food loses its characteristic appearance, and is converted into a white, opaque emulsion, which is gradually absorbed. This emulsion is termed the chyle, and is always found in the small intestine during the digestion of fat, entangled among the valvula conniventes, and adhering to the surface of the villi. The digestion of the oil, however, and its conversion into chyle, does not take place at once upon its entrance into the duodenum, but only after it has passed the orifices of the pancreatic and biliary ducts. Since these ducts almost invariably open into the intestine at or near the same point, it was for a long time difficult to decide by which of the two secretions the digestion of the oil was accomplished. M. Bernard, however, first threw some light on this question by experimenting on some of the lower

animals, in which the two ducts open separately. In the rabbit, for example, the biliary duct opens as usual just below the pylorus, while the pancreatic duct communicates with the intestine some eight or ten inches lower down. Bernard fed these animals with substances containing oil, or injected melted butter into the stomach; and, on killing them afterward, found that there was no chyle in the intestine between the opening of the biliary and pancreatic ducts, but that it was abundant immediately below the orifice of the latter. Above this point, also, he found the lacteals empty or transparent, while below it they were full of white and opaque chyle. The result of these experiments, which have since been confirmed by Prof. Samuel Jackson of Philadelphia,' lead to the conclusion that the pancreatic fluid is the active agent in the digestion of oily substances; and an examination of the properties of this secretion, when obtained in a pure state from the living animal, fully confirm the above opinion.

In order to obtain pancreatic juice from the dog, the animal must be etherized soon after digestion has commenced, an incision made in the upper part of the abdomen, a little to the right of the median line, and a loop of the duodenum, together with the lower extremity of the pancreas which lies adjacent to it, drawn out at the external wound. The pancreatic duct is then to be exposed and opened, and a small silver canula inserted into it and secured by a ligature. The whole is then returned into the abdomen and the wound closed by sutures, leaving only the end of the canula projecting from it. In the dog there are two pancreatic ducts, situated from half an inch to an inch apart. The lower one of these, which is usually the larger of the two, is the one best adapted for the insertion of the canula. After the effects of etherization have passed off, and the digestive process has recommenced, the pancreatic juice begins to run from the orifice of the canula, at first very slowly and in drops. Sometimes the drops follow each other with rapidity for a few moments, and then an interval occurs during which the secretion seems entirely suspended. After a time it recommences, and continues to exhibit similar fluctuations during the whole course of the experiment. Its flow, however, is at all times scanty, compared with that of the gastric juice; and we have never been able to collect at most more than five or six drachms during a period of several hours. Bidder and Schmidt obtained

'American Journ. Med. Sci., Oct. 1854.

on an average, from a dog weighing 44 pounds, 14 grains of pancreatic juice per hour; and they calculate from this that the average daily quantity in the human subject is rather less than 2500 grains, or a little over one-third of a pound avoirdupois.

Pancreatic juice obtained by the above process is a clear, colorless, somewhat viscid fluid, with a distinct alkaline reaction. Its composition, according to the analysis of Bidder and Schmidt, is as follows:

The most important ingredient of the pancreatic juice is its organic matter or pancreatine. It will be seen that this is much more abundant in proportion to the other ingredients of the secretion than the organic matter of any other digestive fluid. It is coagulable by heat; and the pancreatic juice often solidifies completely on boiling, like white of egg, so that not a drop of fluid remains after its coagulation. It is precipitated, furthermore, by nitric acid and by alcohol, and also by sulphate of magnesia in excess. By this last property, it may be distinguished from albumen, which is not affected by contact with sulphate of magnesia.

Fresh pancreatic juice, brought into contact with oily matters at the temperature of the body, exerts upon them, as was first noticed by Bernard, a very peculiar effect. It disintegrates them, and reduces them to a state of complete emulsion, so that the mixture is at once converted into a white, opaque, creamy-looking fluid. This effect is instantaneous and permanent, and only requires that the two substances be well mixed by gentle agitation. It is singular that some of the German observers should deny that the pancreatic juice possesses this property, of emulsioning fat, to a greater extent than the bile and some other digestive fluids; and should state that although, when shaken up with oil, outside the body, it reduces the oily particles to a state of extreme minuteness, the emulsion

is not permanent, and the oily particles "soon separate again on the surface." We have frequently repeated this experiment with different specimens of pancreatic juice obtained from the dog, and have never failed to see that the emulsion produced by it is by far more prompt and complete than that which takes place with saliva, gastric juice, or bile. The effect produced by these fluids is in fact altogether insignificant, in comparison with the prompt and energetic action exerted by the pancreatic juice. The emulsion. produced with the latter secretion may be kept, furthermore, for at least twenty-four hours, according to our observations, without any appreciable separation of the oily particles, or a return to their original condition.

The pancreatic juice, therefore, is peculiar in its action on oily substances, and reduces them at once to the condition of an emulsion. The oil, in this process, does not suffer any chemical alteration. It is not decomposed or saponified, to any appreciable extent. It is simply emulsioned; that is, it is broken up into a state of minute subdivision, and retained in suspension by contact with the organic matter of the pancreatic juice. That its chemical condition is not altered is shown by the fact that it is still soluble in ether, which will withdraw the greater part of the fat from a mixture of oil and pancreatic juice, as well as from the chyle in the interior of the intestine. In a state of emulsion the fat, furthermore, is capable of being absorbed, and its digestion may be then said to be accomplished.

We find, then, that the digestion of the food is not a simple operation, but is made up of several different processes, which commence successively in different portions of the alimentary canal. In the first place, the food is subjected in the mouth to the physical operations of mastication and insalivation. Reduced to a soft pulp and mixed abundantly with the saliva, it passes, secondly, into the stomach. Here it excites the secretion of the gastric juice, by the influence of which its chemical transformation and solution are commenced. If the meal consist wholly or partially of muscular flesh, the first effect of the gastric juice is to dissolve the intervening cellular substance, by which the tissue is disintegrated and the muscular fibres separated from each other. Afterward the muscular fibres themselves become swollen and softened by the imbibition of the gastric fluid, and are finally disintegrated and liquefied. In the small intestine, the pancreatic and intestinal

'Lehmann's Physiological Chemistry. Philada. ed., vol. i. p. 507.

juices convert the starchy ingredients of the food into sugar, and break up the fatty matters into a fine emulsion, by which they are converted into chyle.

Although the separate actions of these digestive fluids, however, commence at different points of the alimentary canal, they afterward go on simultaneously in the small intestine; and the changes which take place here, and which constitute the process of intestinal digestion, form at the same time one of the most complicated and one of the most important parts of the whole digestive function.

The phenomena of intestinal digestion may be studied, in the dog, by killing the animal at various periods after feeding, and examining the contents of the intestine. We have also succeeded, by establishing, in the same animal, an artificial intestinal fistula, in gaining still more satisfactory information on this point. The fistula may be established, for this purpose, by an operation precisely similar to that already described as employed for the production of a permanent fistula in the stomach. The silver tube having been introduced into the lower part of the duodenum, the wound is allowed to heal, and the intestinal secretions may then be withdrawn at will, and subjected to examination at different periods during digestion.

By examining in this way, from time to time, the intestinal fluids, it at once becomes manifest that the action of the gastric juice, in the digestion of albuminoid substances, is not confined to the stomach, but continues after the food has passed into the intestine. About half an hour after the injection of a meal, the gastric juice begins to pass into the duodenum, where it may be recognized by its strongly-marked acidity, and by its peculiar action, already described, in interfering with Trommer's test for grape sugar. It has accordingly already dissolved some of the ingredients of the food while still in the stomach, and contains a certain quantity of albuminose in solution. It soon afterward, as it continues to pass into the duodenum, becomes mingled with the debris of muscular fibres, fat vesicles, and oil drops; substances which are easily recognizable under the microscope, and which produce a grayish turbidity in the fluid drawn from the fistula. This turbid admixture becomes thicker and thicker from the second to the tenth or twelfth hour; after which the intestinal fluids become rapidly less abundant, and finally disappear almost entirely, as the process of digestion comes to an end.

The passage of disintegrated muscular tissue into the intestine