This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
It is well known that, in the course of various diseases, matters accumulate in the blood, either altogether foreign to that fluid, or existing in it during health only in almost inappreciable quantities, and in the course of spontaneous elimination from the system. Thus, urea and uric acid, which are the results of the disintegration of the tissues, or the superfluous residue of the food in its conversion into blood, are, in the healthy state, present in the circulation only until they can be thrown off by the kidneys; and the same may be said of the colouring matter of the bile, which is separated and excreted by the liver. These accumulate abnormally in the blood, when their respective emunctories fail in their office of excretion, and become sources of inconvenience and danger. It is highly probable that other noxious principles, not well understood, in like manner vitiate the blood, either forming special diseases or complicating those resulting from other causes. In febrile complaints, a sour odour is often observable in the breath and perspiration, arising from the escape of acid matters bom the blood. In typhus fever, smallpox, and many cases of disordered digestion and obstinate constipation, the breath and other secretions have an offensive odour, indicating, no doubt, an impure condition of the circulating fluid. Now the existence of such morbid matters in the blood affords a well-grounded indication for the use of remedies calculated to effect their elimination; and there can be no doubt that this is not infrequently a very useful therapeutic process. The remedies alluded to are such as stimulate the several emunctories; and cathartics, diuretics, diaphoretics, and cholagogues. add this mode of action to their other beneficial influences in disease.
There is another mode of elimination which has recently begun to attract attention, and which may possibly hereafter prove a highly important method of cure. It has been shown that certain substances, having a noxious influence upon the health, are sometimes incorporated with the tissue of the organs, and probably thus impair their efficiency by a constant unhealthful influence. Such are various metallic poisons, as the preparations of arsenic, lead, copper, and mercury. To separate these from their seat in the tissues is an important indication; and there is reason to believe that this may sometimes be fulfilled, not only by medicines calculated to promote absorption and secretion, or to alter the nutrition of the organ, but also by others which modify the condition of the foreign matter, so as to render it soluble in the blood, and thus capable of being eliminated from the system. It is believed, for example. that lead is thus displaced, when producing colica pictonum or paralysis, by the exhibition of iodide of potassium. More will be said on this subject under the head of the several remedies employed on the principle referred to.