Chapter CL: Iii.—medicines Which Act Primarily on the Stomach and Primæ Viæ,

AND _SECONDARILY_ ON THE ABSORBENTS.

1. _By diminishing arterial action, and increasing that of Absorption._

1. _Digitalis._

2. _Nicotiana._

2. _By increasing the tone of the Body in general, and that of the
absorbent system in particular._

_Bitter Tonics_, _&c._ _&c._

3. _By producing Catharsis, and thereby increasing the action of
the Exhalants_ directly, _and that of the Absorbents_
indirectly.

1. _Elaterium._

2. _Jalap_, _&c._ _&c._

C. 1. OF MEDICINES WHICH ACT PRIMARILY ON THE URINARY ORGANS.

1. _By stimulating the secreting vessels of the kidneys, by actual
contact._

_a_ The substance not undergoing any decomposition _in
transitu_.

It is easy to imagine that any substance which is capable of entering the current of the circulation, and of stimulating the kidneys by a direct application to their secerning vessels, may occasion a more copious urinary discharge; in this manner the different saline[157] preparations, _Potass_, _Soda_, _Nitrate of Potass_, _&c._ are brought to the kidneys in the course of the circulation, and exciting the vessels to an increased action, promote the secretion of a larger proportion of watery fluid from the blood, in consequence of which, the absorbents are indirectly stimulated in order to supply the deficiency, and in this manner dropsical swellings are reduced.

Water, as a simple diluent, will promote the action of the kidneys, and it is very judiciously remarked by Dr. Cullen, that by withholding the use of fluids in dropsy, you will diminish the quantity of fluids secreted, and allow the secretories of the kidneys to fall into a state of inactivity and collapse. This is a sufficient answer to those who defend the practice of enjoining an abstinence from all drinks in dropsy.

b. _The diuretic remedy undergoing decomposition_ IN TRANSITU.

The digestive organs appear to possess the power of readily decomposing all saline compounds into which _vegetable_ acids enter as ingredients, and of eliminating their alkaline base, which, being in the course of the circulation, carried to the kidneys, excites them into action, and promotes the excretion of urine; and it is probably in this way that the _Acetate_, _Citrate_, _Super-tartrate_, and other analogous combinations of _Potass_ and _Soda_ prove diuretic: on the other hand, it is equally evident that salts containing the _mineral_ acids are not under the control of the decomposing powers of the _chylo-poietic_ organs, and consequently do not undergo any changes _in transitu_, although some of these salts, as I have just stated, especially the more soluble ones, are absorbed entire, and prove diuretic. _Sulphate of Potass_, from its insolubility, is not readily absorbed, and its composition will not allow the developement of its base; we perceive therefore that it has not any tendency to produce an influence upon the urinary secretion.

Certain vegetable bodies likewise appear to occasion diuresis by a similar mode of operation, and it is worthy of notice that these medicines generally contain a bitter principle, which is probably separated by the analysing powers of the stomach; as exemplified in _Scilla maritima_; _Colchicum autumnale_; _Lactuca Virosa_; _Gratiola officinalis_; _Spartium Scoparium_ (Summitates); _Juniperus communis_; _Copaifera Officinalis_ (Balsamum,) &c. The stimulant powers of a bitter vegetable principle upon the _primæ viæ_, have already been fully noticed under the consideration of TONICS, (_page 78_), and it is reasonable to suppose, that an analogous principle, if introduced into the circulation, may exert a corresponding impulse upon the organs with which it comes into contact.

It particularly merits attention, that the diuretic operation of any body that acts by being absorbed, is at once suspended if catharsis follows its administration, whether in consequence of the largeness of its dose, its increased solubility, or from the effect of its combination with some purgative; for it is a law, _that the processes of assimilation, and absorption from the duodenum, are arrested, or very imperfectly performed during any alvine excitement_; the different effects of the saline compounds of the alkalies with tartaric acid, elucidate the truth of this law in a very striking manner—thus, _Super-tartrate of Potass_, or Cream of Tartar, in well regulated doses, acts, as we all know, upon the kidneys; the tartaric acid being, as I suppose in this case, abstracted and assimilated by the digestive process, and at the same time the alkaline base (Potass) eliminated, and subsequently carried into the circulation; but if we increase the solubility of the compound, by reducing it to the state of a neutral tartrate (_soluble tartar_), or by combining it with _Boracic acid_, or some body that has a similar effect; or what is equivalent to it, if we so increase the dose[158] of the _cream of tartar_, that full catharsis follows its administration, then diuresis will not ensue, since no decomposition can take place under such circumstances, nor can it be carried by absorption into the circulation. _Nitre_ and those salts which are carried to the kidneys without previous decomposition _in transitu_, are subject to the same law; for, if we combine them with purgatives, their presence can no longer be recognised in the urine, as I have ascertained by experiment. _Oil of Turpentine_ in doses of two fluid-drachms, may so excite the urinary organs as to produce even bloody urine; whereas a fluid-ounce will scarcely occasion any apparent influence upon those functions, because the increased dose acts upon the bowels, and consequently prevents its passage into the circulation.

_Sulphate of Magnesia_ does not readily produce any diuresis, because it operates upon the bowels, but the experiments of Vitet and Bracy Clarke have shewn, that if this saline compound be administered to the horse whose bowels are not easily affected by purgatives, it acts powerfully upon the kidneys;[159] and I will take occasion in this place to observe that, on account of the inirritability of the bowels of the horse, diuretic medicines are more certain in their operation, than in the human subject; a fact which, in itself, shews the importance of attending to the state of the bowels, during a course of those diuretics which require to be absorbed before they can produce their specific effects.

Equally necessary is it to attend to the state of the vessels of the skin, for if during the administration of a Diuretic, these vessels be excited by external warmth, its action may be diverted from the urinary organs to the exhalants on the surface, and occasion diaphoresis; but if the surface of the body be kept cool, this diversion will not occur: so greatly indeed does cooling the surface determine to the kidneys, that the usual diaphoretic medicines may, by an attention to this circumstance, be converted into powerful diuretics.