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 alimentary canal, named the thoracic duct, being a tough membranous channel, situate upon the interior part of the spine, of about the diameter of a crowquill in man, and running in a serpentine direction through the diaphragm or midriff to an angle formed by an 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 intimately 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.* : *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 hence, the porosity of these vessels was a doctrine in common belief till 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 The simplest action, perhaps, that is evinced by the mouths of the secretory 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 axle-tree of our carriagewheels; 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 carcase; 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 for a fresh and perpetual effusion; whence these vessels are often called LYMPHATIC, as well as absorbent, in consequence of their being so frequently found 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 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. edit. 2d. 1825. 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, in 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 absorbents, 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 |
