IRON AND ZINC.	469
	stools, which they blacken. The Iron meets intestinally with sulphuretted hydrogen generated by fermenting excrementitious matters, and a black sulphide of iron is formed. In this latter case, just as in the former, some salutary influence which materially is inappreciable must be wrought by the Iron on the blood-making organs, and functions. That such Iron proves powerfully astringent when employed by either of these methods cannot be denied ; also that it will promote the increased production of red blood-corpuscles ; though by what exact process is not known : most probably by some occult energy affecting the bodily part with which the metal (infinitesimally volatilised) comes into contact, whether when taken medicinally into the body, or when applied as a compound mineral to its outside. Iron was administered for curative purposes several centuries before Pliny's time. In this country Sydenham was the first (1665) to point out these very important therapeutic pro­perties of Iron as a blood-making power. " To the worn-out, and languid blood," said he, " it gives a spur or fillip, whereby the animal spirits, which before lay prostrate, or sunk under their own weight, are roused, and excited." Regarding Zinc: if a piece of silver wire, (or a silver probe) be introduced high up into one of the nostrils, and have its lower end brought into contact with a small strip of Zinc plate, placed under the tongue, then a sensation not unlike that of a strong flash of light will be produced in the eye on the same side. Or, a similar perception, as though of some pungent taste, will be produced at the moment of contact between the two said metals, if one be inserted high up between the upper lip and its gum, whilst the other is applied in like manner between the lower lip, and the lower gum, or