EXP. 3.--Six drachms of the same salt were given in eighteen ounces of water to the same patient. After a few hours, it caused very copious and long-continued watery purging. The urine did not seem to be increased, and contained no excess of magnesia. It seemed, that in spite of the dilution, the quantity of the salt was so large, that it could not pass off by the kidneys, and so was eliminated from the blood by the bowels, in the same way as other purgative medicines. (_Vide_ Chap. IV.)
EXP. 4.--This trial was the reverse of the last. Two scruples of Acetate of Potash were dissolved in three drachms of water, and thus administered. The solution then contained about twenty per cent. of the salt. According to the endosmotic theory, it should have caused only slight purging, on account of its density. It did not do so, but produced diuresis. The dose was so small, that after absorption it was easily eliminated by the kidneys.
These experiments are in favour of my views, and seem, as far as they go, to cast discredit on the theory of Poisseuille. It will be very easy to multiply them, so as to place the fact beyond a doubt.[24]
This point being so far settled, and there being no physical reason why any other soluble mineral substance should not be absorbed--it being, moreover, proved, by repeated experiments, that they all pass into the blood, we therefore proceed to the second class of bodies capable of absorption.
2. Mineral substances soluble in acids.--It is apparent that if any insoluble substance will admit of easy solution in the fluids of the stomach and intestines, it may be brought to the condition of a soluble one and thus absorbed. Now the gastric juice is acid. This secretion has been variously ascribed to free hydrochloric, acetic, phosphoric, and lactic acids; also to an acid phosphate or lactate of magnesia. There seems to be most reason to conclude that it is lactic acid, which would be easily formed out of the constituents of the food.[25]
But we have now only to regard the gastric juice as containing a free acid. This would reduce to solution the carbonates and oxides of all the metals; less perfectly when anhydrous, more easily when in the hydrated form. In this manner are absorbed the oxides of Iron and Silver, the carbonates of Lime and Magnesia, and other medicines of the same kind. They would be slightly modified, being absorbed in combination with the (lactic) acid of the stomach. In this they would differ somewhat from the substances already soluble, which would probably be absorbed unchanged, unless we except the alkalies and their carbonates, which might be similarly decomposed. Even these, if given in solution, would probably be absorbed faster than the gastric acid could be secreted to neutralize them.