Now beside experiment, it is in vain to attempt against it by Philosophical argument, it being an occult quality, which contemns the law of Reason, and defends it self by admitting no reason at all. [SN: _How_ (_possibly_) _the stomack of the_ Ostrich _may alter Iron_.] As for its possibility we shall not at present dispute; nor will we affirm that Iron ingested, receiveth in the stomack of the _Ostrich_ no alteration at all; but if any such there be, we suspect this effect rather from some way of corrosion, then any of digestion; not any liquid reduction or tendance to chilification by the power of natural heat, but rather some attrition from an acide and vitriolous humidity in the stomack, which may absterse and shave the scorious parts thereof. So rusty Iron crammed down the throat of a Cock, will become terse and clear again in its gizzard: So the Counter which according to the relation of _Amatus_ remained a whole year in the body of a youth, and came out much consumed at last; might suffer this diminution, rather from sharp and acide humours, then the strength of natural heat, as he supposeth. So silver swallowed and retained some time in the body, will turn black, as if it had been dipped in _Aqua fortis_, or some corrosive water, but Lead will remain unaltered; for that mettal containeth in it a sweet salt or sugar, whereby it resisteth ordinary corrosion, and will not easily dissolve even in _Aqua fortis_. So when for medical uses, we take down the filings of Iron or Steel, we must not conceive it passeth unaltered from us; for though the grosser parts be excluded again, yet are the dissoluble parts extracted, whereby it becomes effectual in deopilations; and therefore for speedier operation we make extinctions, infusions, and the like, whereby we extract the salt and active parts of the Medicine; which being in solution, more easily enter the veins. [SN: _What the Chymists would have by their_ Aurum Potabile.] And this is that the Chymists mainly drive at in the attempt of their _Aurum Potabile_; that is, to reduce that indigestible substance into such a form as may not be ejected by siege, but enter the cavities, and less accessible parts of the body, without corrosion.