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duly prepared into chyle until it has been subjected to the action of intestinal secretion, and been operated upon by the fluid from the liver and the pancreas.
That the due supply of bile is absolutely necessary to the formation of chyle, has been satisfactorily proved by the recent experiments of Mr. Brodie, who tied a ligature round the duct which leads, as it has been stated, from the liver into the duodenum ; and in every case, he found that the consequent interruption of the flow of bile into the intestine was attended by an imperfection in the chyliferous change. That the pancreatic secretion is likewise requisite, is demonstrated by the emaciation consequent upon disease in the pancreas. We may bere advert to a very curious observation made by Dr. Monro, of which we are surprised to find no mention made in any of the works before us : it is, that the bile is secreted in larger quantities after a meal than at other times; the final cause of which appears sufficiently evident. "I attended,' says Dr. Monro, "a case in which there was an abscess in the liver, and ia preternatural communication between that organ and the • lungs, through which the bile was secreted and discharged • by coughing. The quantity thus discharged was very diffe* rent at different times. It was always greater after meals, ' and especially for an hour or two after dinner. The celebrated Bichat also proved the same fact by experiments on animals. This physiologist informs us, that the bile which is secreted during abstinence, is divided between the duodenum and the gall-bladder; and that the portion of it which passes into the latter by the channel above described, becomes of a more active quality; it receives, according to the expression of Bichat, 'un charuclére d'âcreté, une teinte foncée. It will readily occur to the reflective reader, how influential, therefore, the number and quantity of meals must necessarily prove upon the quantity and kind of bile that is given out from its organ of secretion upon the alimentary mass ; and consequently, how important regularity of diet must be towards regularity in the process of assimilation. Occasional abstinence too, by causing a greater supply of bile to the gall bladder, in which organ it seems to gain more stimulant properties, may be useful, partly, at least, on this principle, in certain disordered conditions of the digestive organs.
Let us suppose chyle to be formed, and it becomes an interesting question, how far its absolute nature or composition has been modified by the materia alimentaria, as well as by the more or less vigorous or perfect state in which the organization may have been that is concerned in its productions. On
this head we shall avail ourselves of an extract from the work of Dr. Paris.
• When perfectly formed chyle, as that obtained from the thoracic duct, is chemically examined, it will present a difference in composition, according to the nature of the aliment from which it was elaborated. If the animal has eaten substances of a fatty nature, the chyle will be found milky white, a little heavier than distilled water, with a strong and peculiar odour, and a saline and sensibly alkaline taste ; but if the food should not have contained fat, it will be opaline and almost transparent. Very shortly after chyle is exo tracted from the living animal, it becomes firm and almost solid ; it then gradually separates into three distinct parts; the one solid, which remains at the bottom of the vessel, the second liquid, and a third that forms a very thin layer at the surface. The chyle at the same time assumes a rose colour. Of the three parts into which chyle thus spontaneously resolves itself, that on the surface, of an opaque white, and which imparts to the fluid the appearance of milk*, is a fatty body. The solid part, or coagulum, seems to be an intermediate substance between albumen and fibrin, for it unites several properties which are common to the two : it wants the fibrous texture as well as the strength and elasticity of the fibrin of the blood ; it is also more readily and completely dissolved by caustic potass. The liquid part of chyle resembles the serum of the blood. The proportion, however, of these several parts varies according to the nature of the food. There are species of chyle, such as that from sugar, which contain very little albuminous fibrin ; others, such as that from flesh, contain more. The fatty part is very abundant where the food has contained grease or oil, while there is scarcely any under other circumstances.
• These observations, continues our Author, are of great value to the physiologist as well as to the pathologist, as they demonstrate the fallacy of that proposition which has been so frequently advanced, viz., " that there are many species of food, but only one aliment;" intimating thereby, that all substances by decomposition contribute to form one identical, invariable, essentially nutritive principle the “ quod nutrit” of ancient authors; whereas nothing is more clear, than that the nature and composition of the chyle vary with each individual aliment.'
This chyle thus prepared, first by the action of the salivary secretions, secondly and mainly by the gastric juice, and thirdly by the fluids that are poured into the duodenum, is gradually propelled downwards, in connexion with the matter that afterwards becomes separate and effete, till it arrives at that portion of the intestinal tube which we have described as
* The comparison which has been established between chyle and milk, has no real foundation ; for the former contains nothing which exactly agrees with the constitution of the latter.
furnished with those curious vessels, or rather the openmouthed commencement of them, which are called lacteals. These are endowed with a remarkable power both of selection and of transmission; of selecting the chyliferous from the feculent portion of the digested aliment, and of transmitting it through the glands of the mesentery, for still further change, on to the circulation. And now, having thus traced the assimilating material from its reception by the mouth to its reception by the blood vessels, it falls in order that we should allude to the connexion that obtains between the digestive and other functions.
For this purpose it will be necessary to complete our anatomical and physiological sketch of the stomach and its appendages, by pointing out in a very general manner, the mode in which the digestive organization is supplied with nerves and blood vessels ; a particular to which we find none of our authors advert in the manner which might have been expected.
The nerves, which are more immediately derived from or connected with the brain, are principally those which supply the organs of sense. But there is one pair, the eighth, and two others, the fifth and sixth, which, besides supplying these organs, send branches down to form extensive communications with that part of the nervous organization which, under the denomination of the great sympathetic, supplies the stomach, the heart, the liver, and in fine, all the viscera of the chest and abdomen; so that an intimate association of parts and functions obtains, in such sort that integrity in the action of one organ goes far towards effecting a general harmony; while, on the other hand, a disordered state of one part must necessarily, in a greater or a minor degree, interfere with this harmony. Then again, see how the stomach is connected in its blood-vessels with other parts of the organization. Almost directly as the large descending blood vessel from the heart emerges through the diaphragm, the large artery called the celiac comes off, branches of which supply at once the stomach, the upper part of the intestines, and all the contiguous viscera. And there is one particular especially observable in reference to this head, viz. that the spleen, an organ which we have not hitherto named, seems to serve as a reservoir to the blood-vessels of the stomach, and to supply this last organ with a greater or smaller quantity of the vital fluid according to the necessities of the case.
The spleen is a soft spungy substance, exceedingly vascular in its structure, and of a purplish hue. Its size and shape are different in different subjects; it is most generally, however, of an oval form, and about five or six inches in length; lying just under the left extremity of the stomach, to which and to the pancreas it is fixed by means of blood vessels. This organ is, in fact, a collection of blood-vessels, absorbents, and nerves, intermixed with cellular texture; and as it has no excretory duct, like the liver or the pancreas, it is natural to inquire for what purpose it is intended.
From the cæliac artery of which we have just spoken, a large branch, called the splenic, runs on to this organ; but, as it proceeds to its destination, branches are sent off from it to the pancreas, and to a portion of the stomach. So that, in reference to the structure and economy of the spleen, two circum. stances are especially worthy of remark; first, that its bloodvessels are among the largest of the body in proportion to the organ they supply; and secondly, that its blood vessels have a very intimate union with those of the pancreas and stomach.
Now the time at which the stomach is most distended with food, is precisely the time in which a greater than ordinary supply of blood is demanded for the organ; and the stomach is so situated in reference to the spleen, that its distension by aliment, pressing upon the splenic artery, and thus causing an impediment to its current, directs more through those vessels which go to the pancreas and to the stomach itself. Thus, as we have seen that more bile is prepared and transmitted in proportion as more chyme is awaiting its influence, so, more blood is directed to the stomach by the very circumstance which creates the larger want. On this beautiful portion of the assimilating economy, we should have expected that writers on digestion would dilate more largely than we find the authors before us have done. There have been, indeed, some objections started respecting the absolute correctness of the principles now propounded ; but, in the main, we believe the inferences that have been deduced, will be found borne out by an examination of all the particulars connected with the chyliferous process. It strikes us, indeed, that the secretion of bile itself, as regulated by the demands of the stomach, may be greatly dependent upon the arrangement of blood-vessels now alluded to; since the hepatic artery, which is a branch of the cæliac, has necessarily a considerable relation with the other ramifications from the same source. We are aware, that it is chiefly from the portal vein, and not from the hepatic artery, that the bile is thought to be derived ; but the more or less vigorous action of the liver, and consequently the kind and quantity of bile that is formed, cannot fail of having considerable reference to the degree of force with which even the arterial blood is transmitted to the organ. But
we must not pursue this very curious path of research, lest it lead us too far beyond the prescribed limits of the present discussion.
If, then, the process of digestion has to do, both immediately and remotely, both mechanically and sympathetically, with other functions, how interesting is it to trace the sympathies and connexions of the stomach, by taking a general and combined view of the whole organization!
'All my philosophy,' says some author, with which I had been so deeply interested in the forenoon, appears non'sense and confusion to me after I have dined.' Why is it so ? Partly because both nervous energy and circulating impetus are directed from the brain to the stomach and its immediate dependencies. And this, by the way, may account for that chilliness which weakly individuals are sensible of after meals ; which is vulgarly deemed a sign of health, but which ought rather to be put down in proof that the digestive process is going on regularly. And, in this sense, it is a signal of health; but then it is the most feeble who are the most sensible of this vicarious action of one part of the frame for another, upon principles that are sufficiently obvious.
Then, again, with regard to the connexion of the respiratory with the digestive function; the derangement of the one occa. sions the derangement of the other. This connexion may be in some degree mechanical, since a distended stomach interferes with the free action of the diaphragm, and consequently with freedom in respiration. But it is partly, and perhaps principally, médiate and sympathetic, since, as Dr. Paris properly remarks, the lungs are supplied with a part of the nerve of the eighth pair, and some filaments of the sympathetic, which will account for the sympathies which subsist between the • respiratory and the digestive organs. To the same source we may attribute that remarkable relationship which is so frequently manifested between irregularity of the heart and deranged state of the stomach. Indeed, there is no organ or part that has not more or less of this dependence upon the state of the stomach : the kidneys and external surface of the body in a very marked manner exemplify this fact. The experiment of Lavoisier and Seguin have ascertained, that the cutaneous transpiration, or, as we call it, perspiration, is at its minimum during chymification, and at its maximum after the completion of that process. And certain kinds of eruptions on the skin are so manifestly dependent upon what has been received into the stomach, that an emetic which shall cause the ejection of its contents, shall immediately occasion the subsidence of the cutaneous disorder.
It has been above remarked, that the nervous and vascular