a few weeks or months under these circumstances, only proves that nutrition may take place to some extent without chyle being formed. In my experiments I found that the more fluid parts of the chyme had been absorbed, and probably this would have been sufficient to maintain life during a limited period of time.'

It seems then, upon the whole, sufficiently evident that the fluid secreted by the liver, and transmitted into the duodenum, has a very considerable influence towards completing the process of chyle formation; there are some other notions respecting the office of this great viscus in the animal economy which are probably somewhat more hypothetical, but yet do not seem destitute of foundation, we mean that, like the lungs, it helps to rid the system of carbon. It is to be recollected that it is only to these two viscera, the lungs and the liver, that venous blood, blood charged with carbon, is transmitted; and it is matter of common observation that bilious diseases are most frequent in hot climates and seasons, which is attributed to the greater abundance of the bile in those times and circumstances, when less carbon passes off by the lungs, there not being so much occasion for the absorption of heat into the frame. Conformably to this theory it has been remarked, that in the fœtus, for whose temperature the mother's heat must be sufficient, the lungs perform no function, but the liver is of great size, and bile is secreted abundantly, so that the meconium accumulates considerably during the latter months of pregnancy. We shall see, indeed, that at the very time the functions of the lungs suddenly begin at birth, the liver suddenly loses so much of its supply of blood. Warm-blooded animals with large lungs, living in the air, have the liver proportionably smaller than those which live partly in water; in cold-blooded animals and reptiles, which have lungs with large cells, as but slightly to decarbonise the blood; in fish, which get rid of carbon but slowly by the gills; and in the molucca, which decarbonise still more slowly by gills or lungs, the liver is proportionally large. More blood flows to the liver accordingly as the lungs are less active organs. In the mammalia and birds it receives the blood of only the stomach, intestines, spleen, and pancreas; but, in the cold-blooded, of many other parts; in the tortoise of the hind legs, pelvis, tail, and vena azygos; in serpents of the right renal, and all the intercostal veins; in fish of the renal veins, the tail, and genitals. It is moreover said that in pneumonia and phthisis more bile is secreted; and in the blue disease, and other affections of the heart, that the liver is enlarged. The constituents of the bile contain a large quantity of carbon, which is chiefly in union with hydrogen, and under the form of resin or fatty matter, and resin is most abundant in the bile of herbivorous animals, whose food contains a very large proportion of carbon and hydrogen. In the lungs the carbon may be said to be burnt, whence animal heat; in the abdomen it passes off still com

bustible.'

Of the use of the spleen. This still continues to be a physiological problem. That a large Viscus should be found without any obvious in

tention seems extraordinary, and Dr. Paley, when he is treating on final causes, suggests 'that it may be merely a stuffing, a soft cushion to fill up a vacuum or hollow, which, unless occupied, would leave the package loose and unsteady;' thus supposing, as Dr. Elliotson wittily and sarcastically states it, that a pad is necessary to make the viscera fit, just as hatters put stuf fing under the leather of a hat which is made too big for the head. When,' he adds, 'I consider the stupendous power and design displayed throughout nature, I instantly revolt at such an explanation as Paley's, to say nothing of its anatomical absurdity.'

The most generally entertained opinion of the office of this viscus is that it proves subservient to the stomach and liver, by collecting blood for the purpose of being sent to these last organs when a more than ordinary supply is required; and this inference has been drawn from the mode in which the blood-vessels of the spleen are connected with those of the liver and stomach; this last organ, when it is full, not only compressing the spleen by its distension, but, from the very same pressure, causing a diversion of blood from the spleen to itself. Mr. Pring, we believe, in a work of great originality, was the first to combat this supposition, and to maintain that we have no proof that the repletion of the stomach effects any material compression on the spleen and its blood-vessels, so as to alter the circulation. Besides, in ruminating animals, as Blumenbach observes, it lies next the first stomach or paunch, and, if compressed, must be so before digestion begins; and in proportion as the fourth stomach fills, and digestion proceeds more actively, is the distension of the paunch diminished."

Sir Everard Home conceived that a great proportion of the liquid which disappears from the stomach might get from the cardiac extremity of this organ into the spleen, and thence into the mass of blood; but from later experiments he has been induced to abandon this hypothesis, and the real office of the spleen still continues among the arcana of nature. It is, however, most probably connected in some way with the digestive and assimilating functions, and it is a remarkable fact, long ago observed, that the extirpation of this organ sometimes renders the bile in the gall bladder pale and inert. Some physiologists have recently speculated on the use of the spleen in the lymphatic system; and still more recently it has been thought a secretory organ with a glandular duct, but nothing very satisfactory has been elicited from these views of the subject, and we repeat that more facts are wanting than hitherto we are in possession of to render fully evident the precise use of this viscus in the animal economy.

The omentum would seem principally ordained for the purpose of lubricating the intestines, and assisting their constant motion; but it has been suggested that this also as well as the spleen may serve as a diverticulum to the viscera; if," says Blumenbach, 'we reflect on the singular structure of the omentum parvum or hepatogastrum especially, we may be inclined to believe that there is another, and perhaps principal

office attached to it unknown at present, and discoverable by comparative anatomy.'

Respecting the functions of the large intestines we cannot do better perhaps than present to our readers the following extract from Dr. Capland.

To the functions of the larger intestines may be given the term fæcation, because it is in this situation of the digestive canal that the fæcal matter is found. In its course through the small intestines the alimentary matters are deprived of their chyle, and of a portion of their aqueous parts; the residue is poured into the colon, where its course is more slow, and where it assumes new characters. The fæcal mass, according to the properties which it presents at the commencement of the colon, is evidently composed-1st. Of the residue of the aliments; and 2d. Of the excrementitial parts of the secretions poured into the superior parts of the digestive tube. The fæces, when they arrive in the rectum, or at the time of their expulsion from the body, are greatly increased by the more solid parts of the secretions poured out upon the internal surface of the colon, their more fluid parts having been absorbed. It is in some measure owing to the quantity and properties of the excrementitial parts of these latter secretions, which principally proceed from the follicular apparatus of this intestine, that the fæces present distinctive characters.' Gaseous substances generally are found in greater or less abundance in the small intestines. This gas may come from more than one source; it may arise from the change which the alimentary substances undergo in their course, or it may be secreted by the mucous membrane of the intestines themselves. While we would not altogether deny a share in its production to the former, we contend for the latter. We believe that the mucous membrane of the digestive canal may both secrete gaseous substances and absorb them; and we found our belief upon the following circumstances:-1st. We have proofs, derived from experiment and observation, that gaseous substances are absorbed and given off from the mucous membranes of the respiratory apparatus. 2d. Pathological facts intimately connected with the functions and properties of his membrane, in different parts of the body, support the position. We have, however, no doubt that the changes which the alimentary substances undergo in the stomach occasional y give rise to gaseous products, and we believe that a similar result follows the removal of the excrementitial matters in the colon and rectum.

On the urinary secretion, which the reader will perceive by turning to the table of arrangement Richerand introduces under the head of digestion, we shall have to offer a few remarks when considering the subject of secretion; at present we shall limit ourselves to remarking that the transmission of fluids from the stomach to the urinary organs, and other parts, is a physiological problem that has not been satisfactorily solved.

OF ASSIMILATION AND ABSORPTION. Assimilation and absorption are the processes by which that remarkable characteristic of organic

being, upon which we have commented in the introductory part of the present treatise, is effected and maintained. Our author says that a definition of life might be taken from the singular property which is possessed by a living being of preserving an independence of interior temperature through all the chances and changes of exterior heat; but, besides that this principle and law of living matter is subject to much qualification, it appears to us that life is still better distinguished from inorganic matter by the faculty which it possesses of making dead matter subservient to its own purposes, of attaching it to itself, and occasioning it to become an integral portion of the organised frame.

In respect, however, to the absolute nature and modus operandi of this faculty there is still much of doubt and dispute. Some supposing that the repairing function is exercised through a distinct order of vessels, the lacteals and lymphatics, for which see ANATOMY. Others conceiving that matters are taken up both from without and from internal parts by the blood vessels, more especially the veins; from internal parts we say, for we shall afterwards see, when on the subject of exhalation and secretion, that there is a constant expulsion from the blood of matter, part of which is thrown out of the frame entirely, and part reabsorbed, or again taken up into the circulating mass.

In the section just concluded on digestion, we talked of chyle, and its separations from the effete part of the alimentary mass; but we did not pursue this same chyle on to its ultimate destination, which is that of the blood vessels through the lacteal vessels, opening in the villi of the intestines-the small intestines mainlyand running on into the receptacle of the chyle, to be conveyed by the thoracic duct into the blood vessels at the angle, found by the union of the subilavian and jugular vein.

Now no one doubts that these lacteal vessels are the main instruments through which nutritious matter is conveyed into the blood, and by which nutrition is thus mainly effected; but there are disputes still existing whether their office is actually limited to this function, and whether the other portion of vessels which with the lacteal have been, since the discovery of both of them, considered the vessels appropriated alone to the process of absorption, are in reality such; or whether the old supposition of imbibition or penetration through the coats of the veins of matter from without, the vessels must not be received to enable us to account for all the phenomena attendant upon absorption. Another point of uncertainty, in reference to the function now under notice, is this, whether any matter is taken up from the outer surface and conveyed into the blood-vessels, while the external skin or cuticle remains as an entire covering to that surface. In other words does the surface of the body absorb? It behoves us then in the present section not only to enquire into the rationale of assimilation and absorption, but to advert to these disputed particulars.

In respect to the lacteals and their office, there is something very singular in the selecting power which they manifest; for, although the chyle is

applied to their mouths mixed with other matter, that other matter is rejected by them, and the chyle alone selected. This power indeed is manifested throughout the system of absorbents generally, some substances being chosen, and some left as unfit for reception. Every one has seen marks on the skin of sailors and others, which have been artificially made by pricking holes in the cuticle, and then rubbing into these holes charcoal or gunpowder; and these marks thus made remain permanent, because the absorbent power refuses to take the materials with which they are made into the mass of circulation. Indeed we might give another explanation of this phenomenon, viz. that fluidity being a necessary circumstance for absorption, these substances are not absorbed because they are not soluble in the fluids of the body. But a selecting principle is manifestly in operation throughout the whole absorbing system; and Magendie has contended for this principle, in the lacteals being carried to such an extent, as that they can be made to absorb nothing but chyle; a doctrine, however, which seems disproved by the well known experiments of Mr. John Hunter, who, pouring milk into the intestines of a dog, found the lacteals soon after filled with it. Different matters too will be taken up by the lacteals, carried through the circulation, and afterwards thrown out by emunctories; although, with respect to the extent and nature of this principle, there are confessedly some reasons to be doubtful.

What is the rationale, it is natural to enquire, of the process by which chyle is received into the minute branches of the lacteals, and conveyed on to the blood? That open mouths are exercised in this case at least, and that chyle does not penetrate the coats of the absorbent, has been demonstrated; so that, whatever may be the laws of absorption in other parts of the frame, in this there is not merely a selecting but an imbibing power displayed, and the chyle once received is as it were sucked through the vessels by a vital force, more similar than any other to that of capillary attraction in inanimate nature; but still different: or at least if there be an actual similarity in the mode of drawing up liquids through minute tubes, and the transmission of the chyle through the minute lacteals there is in the latter case a regulating force which must considerably modify the result; and, although it is right to call in the aid of natural philosophy for the explication of living actions, the mistakes which our ancestors have been led into from too largely admitted analogies ought always to be in recollection.

On the mesentery there are numerous glands attached to the lymphatic vessels, and which are so situated that the chyle, in passing on to the blood, traverses them; it is of course natural to suppose that some operation is performed by these glands upon the chyle: a supposition which is strengthened by the fact that although under some forms of disease, as in the mesenteric atrophy of children, the glands in question remain previous for the transmission of the chyle, the body nevertheless becomes emaciated, as if from an insufficient supply of chyle to the blood. These glands are cellular in their construction,

and it is supposed that the matter contained in the lacteals entering into them is poured into these cells, which matter is taken up by the vessels running out of them in the way of absorption, and that thus something more than a mere passage mechanically, as it were, through the gland, is accomplished.

So far then every thing is to a certain degree evident on the function of assimilation. We have seen that a separation of the chyle from effete matter is effected in the upper part of the alimentary tube, and that the former is conveyed by distinct and appropriate conduits on to the blood-vessels. The chemical composition of the chyle we refer to the article CHEMISTRY; here limiting ourselves to saying that the contents of the thoracic duct have been found differently filled, according as the animal upon which the examination is made shall have fasted for a long time, or have lately taken food: in the latter case the fluid is more albuminous, and really chyliferous; in the former it has more of the character of lymph. Does not this circumstance, by the way, in some measure militate against the assumption of Magendie; that it is chyle, and chyle only that the lactiferous vessels will take up?

The lymphatic system of vessels is so similar in appearance to the lacteals that an inference has been made, from this similarity, in favor of their being the exclusive absorbents of the general frame, while the lacteals are principally the absorbents of the chyle. But it must be observed that their open mouths have never yet been discovered, so that when it is stated that they arise by such open orifices from different structures, and take up the fluid which these tissues pour out, we rather talk inferentially than in the way of demonstration.

Besides the chyle separated from the faces in the small intestines, there are the halitus of the cavities, properly so called, especially that of the fauces and of all the mucous tela, the more watery part of those secreted fluids which are retained for some time in their ducts, i. e. in the breast, the vesiculæ seminales, the gall-bladder, &c., and not a small portion of the stellatious fluids, which are applied to the common integuments.

The solids, after performing their purpose in the animal economy, insensibly melt away, and are absorbed, as is proved by the greater part of the thymus gland during infancy, of the roots of the first teeth, and of the alveoli, after the second teeth have fallen out. The constant change of the whole osseous system, arising from the insensible renovation of bony matter, may also be adduced.

Indeed this process of absorption is so constant and so universal, that no part of an organised frame continues to have from day to day the same identity; in the fingers which now direct the pen of the writer not a particle of the same matter probably exists that constituted the structure of the parts a twelvemonth since, and the same mutation is incessantly going on through every part and portion of the frame; an argument has indeed hence been drawn against what is called materialism, since consciousness and identity remain, while the material particles of the body are thus unceasingly running their round of mutations.

We have already intimated that analogy led to the inference that as the lymphatics appear nearly the same in structure and peculiarities as the lacteals, the two systems together constitute the whole of the absorbing system; and this is in truth the generally received doctrine of the present day, more especially in this country, since the anatomy and peculiarities of the lymphatic system have been so ably elucidated by the labors of Hewson, John Hunter, and Mr. Cruickshank.

Some French and American and German physiologists have lately endeavoured to prove that the principal part of absorption is effected through the medium of the veins; thus in some measure reviving the old doctrine of imbibition into the blood, directly through the coats of vessels, and not by a distinct and exclusive system of organs.

The arguments of Magendie and others in favor of venous, as opposed to lymphatic absorption, are shortly the following:-In the first place they urge that the suddenness with which the secretions are sometimes affected is inconsistent with the notion of the course of absorbed fluids through the lymphatic and the thoracic duct (we should perhaps have premised that lymphatic absorption implies this course, since the termination of most of the branches of the lymphatics is into the thoracic duct); and still further they say, that as the urine often becomes tinged in a very short time with turpentine, rhubarb, copaiba, and other substances, while no such tinge is traceable in the lymph contained in the thoracic duct, it would seem that this channel is not their course to the kidneys. To this, however, it may be replied, that the fact militates equally against venous absorption itself, since the round of circulation must be performed equally in one case as in the other, and, moreover the blood is apparently often as free from the impregnation adduced, as the contents of the thoracic duct. Not, however, always.

The objectors further state that, when the thoracic duct of a dog is tied, an infusion of nux vomica injected into the stomach or rectum, kills as quickly as though the ducts were pervious. But in this case the nervous organisation may be the media of transmission; and it is not necessary to suppose any absorption at all for the production of the effect.

But we must here find room for one or two of the positive experiments in favor of the imbibing power of the venous coats, or of the admission of matter into the blood through these coats. A vein was placed in some acid liquor with its two extremities projecting from this liquor; then a stream of warm water was injected through the vein by its orifices, and, after continuing this injection for some time, the current of water which passed out of the lower orifice of the vein was sensibly impregnated with acidity. This fact, then, it is urged, proved a communication between the interior of the vein and the liquid in which its exterior was immersed; indeed, it showed actual venous absorption. But still the lymphatic physiologists reply to this, that the condition of a vessel may be changed by subjection to these trials;

and it does not follow that the coats of a vessel would have thus proved pervious if it had been in its natural condition, and surrounded merely by the exhalations of the living body.

'Three ounces of diluted alcohol were given to a dog; in a quarter of an hour the blood of the animal had a decided smell of alcohol; the lymph of the thoracic duct had none.

'Half a pound of assafœtida dissolved in the same quantity of honey was given to a horse, which was afterwards fed as usual, and killed in sixteen hours. The smell of assafoetida was perceptible in the veins of the stomach, small intestines, and cæcum; but not in the arterial blood, nor in the lymph.'

It is allowed by the same author from whom we extract the account of the last two experiments, that in Fiedemann's and Gmelin's trials, among a variety of substances taken, colored, odorous, or saline, very few could be detected in the chyle, but many were found in the blood.

These and other experiments and observations which might be adduced, did our limits permit, have led to the inference that the only general absorbents are the veins; that the lacteals merely take up the chyle from the food; that the lymphatics are not in reality absorbents; and that the villi of the intestines are composed partly by venous twigs which absorb all the fluids in the intestines excepting the chyle; this last being taken up by the lacteals, and going into the blood through the receptaculum chyle and thoracic duct. It is supposed, moreover, that the intestinal fluids having been received by the veins are carried on to the heart and lungs, having first been conveyed into the liver by the vena portæ, whose function it is minutely to subdivide and mix with the blood the fluids thus absorbed; which subdivision and intermixture is necessary to prevent their proving detrimental.

The physiologists who thus argue against lymphatic absorption suppose the purpose which these vessels serve in the animal economy is that of conveying the finer parts of the blood to the heart, as the veins convey the grosser and colored portion of the fluid. And it must be confessed that their positions and inferences are considerably forcible. But, on the other hand, many facts favor the other side of the question: how, for instance, can we explain the circumstance of a poison inserted into a part of the frame, and running often with great rapidity along the course of a lymphatic trunk, unless this last vessel were possessed of an imbibing power, and its minute extremities had open mouths? A cancer of the breast may be often clearly traced in its progress through the adjoining lymphatics into the lymphatic glands of the axilla; and it is too well known that the extirpation of the diseased part is generally unavailing after the neighbouring glands have thus taken on disordered action, inasmuch as the lymphatic vessels now appear to have absorbed into the system that peculiar something upon which cancer depends; and have converted a topical into a constitutional ailment. Who does not know, also, that mercurial friction is the most availing when performed where the lymphatics and their glands are most numerous? In