ASSIMILATION AND NUTRITION. 153 



tory or secernent vessels, consists in separating and throwing forth a fine 

 lymph from the surface of all membranes and organs whatever, for the pur- 

 pose 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 for a fresh and perpetual effusion : whence 

 these vessels are often called LYMPHATIC, as well as absorbent, in conse- 

 quence 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 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 ves- 

 sels 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 alto- 

 gether on the morbid and predominant excitement of the secements. 



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, notwith- 

 standing 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 de- 

 mands; 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 ves- 

 sels ; 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 intumes- 

 cence or swelling. For under this affection the mouths of the secernent 

 vessels, being more distended than in a natural state, pour forth the coagula- 

 ble lymph in a grosser and less attenuate form, and not unfrequently, per- 

 haps, 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 



