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tables too often supply us with instances of this fact, in dishes of roast or boiled meat too long exposed to the action of the fire, and hence reduced to juiceless and ragged fibres, totally devoid of nutriment, and capable of keeping for weeks or months, without betraying any putrefactive indication. In like manner, when bodies are buried beneath the hot and arid sands of Egypt or Arabia, with a sultry sun shining, almost without ceasing, upon the sandy surface, the heat hereby produced is so considerable as to raise the whole of the fluids of the animal system to the cuticle, whence they are immediately and voraciously drunk up by the bibulous sands that surround it; or, piercing their interstices, are thrown off into the atmosphere in the form of insensible vapour. In consequence of which, when a body thus buried is dug up a few weeks after its interment, instead of being converted into its original elements, it is sound changed into a natural mummy, altogether as hard, and as capable of preservation as any artificial mummy, prepared with the costliest septics employed on such occasions. When dead animal organs are deposited in situations in which only a very small portion of atmospheric air is capable of having access to them, a change indeed takes place, but of a very different description from that of putrefaction, and which is of a most curious and extraordinary nature. For in such cases the animal organs, instead of being converted into their original elements, are transmuted into fat, wax, or spermaceti; or rather into a substance sui generis, and possessing a middle nature between that of the two former, whence the French chemists have given it the appellation of Adipocire; a term not strictly classical, but for which the chemists of our own country have not hitherto substituted any other. This result is observed, not unfrequently, in bodies that are drowned, and rendered incapable of rising to the surface of the water; for in such a situation but very little air, and, consequently, very little oxygen, can reach them from the external atmosphere. And it is to these circumstances we ought, perhaps, to resolve the singular appearance in the body of Colonel Pollen, who was wrecked a few years ago in the Baltic Sea, near Memel, and within sight of the coast; and whose corpse was six months afterward thrown on shore, with the features of the face so little varied, that every one of his acquaintance recognised him at the first glance. The body had probably been entangled in the submarine sands on first sinking, and been retained in this situation for months, cut off from that exposure to external air which is absolutely necessary in all cases of putrefaction properly so called. A similar conversion into wax-fat was observed also in 1786 and 1787, on opening the fosses communes, or common burial pits in the churchyards of the Innocents at Paris, for the purpose of laying the soundation of a new pile of buildings. For the bodies that on this occasion were dug up, instead of being dissolved into their elementary corpuscles, were sound for the most part converted into this very substance of waxy fat or adipocire. The populace were alarmed at the phenomenon, and the chemists were applied to for an explanation. M. Fourcroy, among others, attended upon this occasion; and his solution, which will apply to all cases of a similar kind, referred the whole to the extreme difficulty with which external air had obtained any communication with the inhumed bodies, in consequence of the close adaptation of coffin to coffin, and the compactness with which every pit had been filled up. Difficult, however, as this communication must have been, he conceived that, from the natural elasticity of atmospheric air, some small portion of it had still entered, conveying, perhaps, just oxygen enough to excite the new action of decomposition. This having commenced, the constituent oxygen of the dead animal organs would itself be progressively disengaged, and rapaciously laid hold of by all the other constituent principles, from their strong and general affinity to it. During this gradual evolution, there can be little doubt that the greater part of it would be seized by the predominant azote, a very considerable part by the carbon, and the rest by the hydrogen; and the result would be, upon the total but very slow escape of the constituent and disengaged oxygen, that the whole or nearly the whole of the azote a considerable por

tion of the carbon, and a certain quantity of the hydrogen, would escape also -leaving behind the remainder of the carbon and the hydrogen, now incapable of escape from the want of oxygen to give wings to their flight, together with the residual earth of the animal machine.

But hydrogen and carbon, though in this case incapable of sublimation for want of oxygen, would still, from their mutual attraction and juxtaposi. tion, enter into a new union and produce a new result, and this result must necessarily be fat; for fat is nothing else than a combination, in given proportions, of carbon and hydrogen. And hence, whatever the respective animal organs of the bodies deposited in these burial caverns may have antecedently consisted of, whether museles, ligament, tendon, skin, or cellular substance, when thus deprived of their oxygen and azote, the whole must of necessity be converted into fat. Pure and genuine fat it would have been, provided there had been nothing left behind but mere carbon and hydrogen, and in their respective proportions for the formation of fat; but as we can scarcely conceive such proportions could take place, or that every corpuscle of the azote could be carried off before the total escape of the oxygen, many parts of it must necessarily have assumed a flaky, soapy, or waxy appearance, from the union or the azote left behind with some portion of the hydrogen, and the consequent production of ammonia or volatile alkali; since, by an intermixture of alkali with fat, every one knows that soap or a saponaceous substance is uniformly produced.

But, excepting in situations of this kind, in reality, in every situation in which dead animal matter, destitute of its living principle, is exposed to the usual auxiliaries of putrefaction, putrefaction will necessarily ensue, and the balance will be fairly maintained :--the common elements of vital organization will be set at liberty to commence a new career, and the animal world will restore to the vegetable the whole which it has antecedently derived from it.

In this manner is it, then, that nature, or rather that the God of nature, is for ever unfolding that simple but beautiful round of action, that circle of eternal motion, in which every link maintains its relative importance, and the happiness of every part flows from the harmony of the whole. Can we, then, do better than conclude with the correct and spirited apostrophe of one of our most celebrated poets ?

Look round the world! behold the chain of love
Combining all below and all above.
See plastic nature working to this end;
Atoms to atoms-clods to crystals lend.
Nee dying vegetables life sustain:
See life, dissolving, vegetate again.-
All serv'd, all serving, notbing stands alone,
The chain holds on, and where it ends unknown.

LECTURE XIV.

OR THE PROCESSES OF ASSIMILATION AND NUTRITION; AND THE CURIOUS EFFECTS

TO WHICH THEY LEAD.

We have traced out in our preceding studies something of the means by which form, and magnitude, and motion are produced in the inorganized world :how the various substances that surround us combine and separate, vanish from us and reappear, and, in the multifarious processes they undergo, give rise to new products by new and perpetually shifting involutions. We have farther traced an outline of the means by which organized matter is capable of building up the curious structures of plants and animals; how the chief func.

• This line is altered to answer the present purpose in a better manner.

tions they possess are carried on, and by what means they respectively ac. quire maturity and perfection.

But it is not only necessary that the system should in this manner be matured and perfected by a fresh application of materials, but that the old materials which constitute every organ should be progressively removed from the system, in consequence of their being worn out by use, and their place supplied from definite stores. Let us, then, devote the present hour to an inquiry how this latter change occurs in vascular and living matter, in the vegetable and animal system : by what means the dead or exhausted and worn-out elements of the different organs are carried off, and replaced by new reformative materials, and what are the principal phenomena that result from such a series of operations.

The blood, then, in animals, and the sap, which may be regarded as a spe. cies of blood, in plants, of both which we have already treated, are the vital currents from which every organ of the individual frame derives the nourishment it stands in need of, and into which it pours ultimately a considerable portion of its waste and eliminated fragments; for the provident frugality of nature suffers nothing to be lost, and, as far as possible, works up the old materials, time after time, into fresh food for the subsistence of the entire system.

To produce this double purpose two distinct sets of vessels are necessary : one for that of separating from the common mass of the blood, and recom bining into new associations, those particular parts of it which the formation of the fresh matter demands; and the other for that of carrying back the rejected materials into the general current. And hence these two sets of ves. sels bear the same relation to each other as the veins and arteries of the ani. mal frame, accompany every part of the frame to its farthest extremities, and, indeed, constitute the general mass of the frame itself. From the respective offices they perform, they are denominated SECERNENT and ABSORBENT systems: in their utmost ramifications they are too minute to be traced by the keenest eye, or the nicest experiment of the anatomist; but where they are not quite so minute, they are sufficiently discoverable, and their course is sufficiently capable of being followed up, from the delicate apertures or mouths by which, in infinite numbers, they open on all animal surfaces, or hollows whatever, to their incipient sources.

The sECERNENTS, or that set of vessels whose office it is to separate particular parts from the blood for particular purposes, are evidently continuations of some of those very subtile ramifications of the arteries which, on account of their fineness, are called capillary; and the ABSORBENTS, or that set of vessels whose office it is to imbibe or drink up the waste and exhausted materials, are as evidently distinct and attenuate tubes, progressively uniting, and ultimately emptying themselves into the venous system; the common trunk in which they concentre, and in which also concentre the lacteals of the ali. mentary canal, named the thoracic duct, being a tough membranous channel, situate upon the interior part of the spine, of about the diameter of a crow. quill in man, and running in a serpentine direction through the diaphragm or midriff to an angle formed by a union of the jugular and subclavian veins, into which it opens, and where of course it terminates, leaving the waste and the new food, now ultimately intermixed, to be still farther elaborated and refitted for use by those subsequent and specific operations of the heart and the lungs which we have already described.

The simplest action, perhaps, that is evinced by the mouths of the secre

• This double action by a double set of vessels was little, if at all, known to the ancients, who referred the economy of both secretion and absorption to the powers of peculiar arteries and veins; and bence, the porority of these vessels was a doctrine in common belief ull the time of Hewson, Hunter, and Cruickshank M. Magendie and M. Flandrin, of Paris, have of late been very active in establishing a view of the subject in many respects not essentially different from that of the old school, and in teaching that the only general absorbents are the veins; that the lacteals absorb food, but nothing else; and that the lymphatics have no absorbent power whatever. Their experiments are plausible and striking, but by no means decisive enough to subvert the system explained above. The argument on both sides may be found in the author's Study of Medicine, vol. v. p. 278, 2. edit. 1825.

tory or secernent vessels, consists in separating and throwing forth a fine lymph from the surface of all membranes and organs whatever, for the purpose of lubricating them, as we grease the axletree of our carriage-wheels; and thus preventing one membrane or organ from being injured by the friction of another. Of this every one who has been present on the cutting up of slaughtered oxen must have seen an abundant and striking instance, in the vapour that ascends from every part of the warm carcass: which vapour, when condensed by cold or any other cause, is found to be little more than the serum or watery part of the blood. And one of the simplest actions evinced by the mouths of the absorbent vessels consists in their drinking up, as with a sponge, this attenuate or lymphatic fluid, when it has answered its purpose, so as to make room sor a fresh and perpetual effusion: whence these vessels are often called LYMphatic, as well as absorbent, in consequence o their being so frequently sound loaded with this fine and colourless material. And here, perhaps, the first remark that must occur to every one is, the necessity there seems to exist, that these correspondent systems of vessels should maintain the nicest harmony or balance in their respective functions, since, if the one operate either with a less or a larger power than the other, disease must inevitably follow; the nature of the malady being determined by the nature of the cause that produces it. We have all of us heard, and most of us have seen, instances of the disorder called dropsy; and many of us have surveyed it both in a local and a general form, as dropsy of the head, dropsy of the chest, dropsy of the abdomen, and . dropsy of the cellular membrane or system at large. This disease may take place from two causes; as, for example, from a too great excitement of the secernent system, or a too little excitement of the absorbent. If, from a morbid irritability in the secernent vessels of any one of the cavities I have just adverted to, an undue proportion of lubricating lymph be secreted and steam forth, the natural tone and action of the correspondent absorbent vessels will not be sufficient to carry off the surplus; and hence that surplus will accumulate, and dropsy ensue, although the absorbent vessels of the part affected be in a state of usual health and vigour: the disease depending altogether on the morbid and predominant excitement of the secernents. But suppose the absorbent vessels of a particular cavity, in consequence of cold, exhaustion from great previous exercise, or any other cause, to be rendered torpid and inert, and, consequently, incapable of continuing their accustomed measure of action: in this case, dropsy will also ensue, notwithstanding the corresponding secernent vessels are in a state of natural health, and no larger portion of lymph is secreted than a state of natural health demands; for the fluid will now accumulate, from the morbid torpitude of the absorbent system, and its inability to fulfil its function. It is hence, as every one must perceive, a point of the utmost consequence to determine the nature of the cause in dropsy; as, in truth, it is in every other disease, before we attempt a remedy; since an error upon this subject may be productive of the most serious, and indeed fatal consequences. For it is obvious that we may stimulate where we ought to diminish action, or we may diminish action where we ought to stimulate. - occasionally, however, the action is equally increased in both sets of vessels; as, for example, an inflammation of the leg or arm; and in this case there is great heat and dryness, and at the same time considerable intumescence or swelling. For under this affection the mouths of the secernent vessels, being more distended than in a natural state, pour forth the coagulable lymph in a grosser and less attenuate form, and not unfrequently, perhaps, intermixed with some particles of red blood; while the mouths of the aboorbents, though they as eagerly drink up the finer parts of what is thus rapidly strained off, are incapable of carrying away with equal ease those of a grosser texture; in consequence of which these last remain behind, and produce tumefaction by their accumulation. - - - At times, also, we meet with an equal degree of diminished instead of

increased action in both these sets of vessels; as on exposure to cold and damp temperatures; in cases of spare and coarse diet; or of old age. And the result of this double decrease of energy is dryness, as in the former instance, but combined with leanness and corrugation of the organs that are thus affected. It is hence the bones of old people are more easily broken, and the skin is harsher and more wrinkled than in the middle of life; hence the shrivelled and squalid appearance of gipsies and beggars; and hence, in a considerable degree, the low and stinted stature of the Esquimaux, Laplanders, and Tongooses. For all the usual purposes of health and organic nutrition, the common action and common degree of action evinced by these respondent systems of vessels are perfectly sufficient, though not more than sufficient. It may happen, however, that in consequence of severe violence from external injury or internal disease, a considerable portion of an organ, as a part of some of the muscles that belong to an arm or a leg, may be totally destroyed or killed, and, consequently, rendered incapable of performing its proper function. How is nature, or, which is the same thing, the remedial principle of life, to act in such circumstances ! If the dead part remain, it is manifest that it must impede the living parts that surround it in the execution of their appropriate office: independently of which they want the space which the dead part occupies, and the aid which it formerly contributed. It is obvious that two processes are here necessary: the dead part must be carried off, and its post must be filled up by a substitute of new matter possessing the precise properties of the old. And here we meet with a clear and striking instance of that wonderful instinctive power which pervades every portion of the vital systems, both of the animal and vegetable world, and which is perpetually prompting them to a repair of whatever evils they may encounter, by the most skilful and definite methods. In order to comply with this double demand of carrying off the dead matter, and of providing a substitute of new, each of the systems before us commences, in the living substance that immediately surrounds that which requires removal, a new mode and a new degree of action. A boundary line is first instinctively drawn between the dead and useless, and the living and active parts; and the latter retract and separate themselves from the former, as though the two had been skilfully divided by a knife. This process being completed, the mouths of the surrounding absorbent vessels set to work with new and increased power, and drink up and carry off whatever the material may be of which the dead part consists, whether fat, muscle, ligament, cartilage, or bone; the whole is equally imbibed and taken away, and a hollow is produced, where the dead part existed. At the same time the mouths of the corresponding secernent vessels commence a similar increase and newness of action, and instead of the usual lymph, pour forth into the hollow a soft, bland, creamy, and inodorous fluid which is denominated pus; that progressively fills up the cavity, presses gradually against the superincumbent skin, in the gentlest manner possible distends and attenuates it, and at length bursts it open, and exposes the whole of the interior to the action of the gases of the atmosphere. It was at one time conceived, and by writers of considerable eminence and judgment, and of as late a date as the time of Mr. Hewson, that the injured and dead parts were themselves dissolved and converted into pus; but this opinion has been disproved in the most satisfactory manner by the minute and accurate experiments of Mr. John Hunter, Sir Everard Home, and Mr. Cruickshank; and the process has been completely established as I have now related it. In what immediate way the gases of the atmosphere operate so as to assist the secerment mouths of what is now the clean and exposed surface of a wound, in producing incarnation, or the formation of new matter of the very same kind and power as that which has been carried off, and enable them to fill up the cavity with such new matter, and perfect the cure, we do not exactly know. Various theories have been offered upon this very curious subject;

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