For the Brisles of a Hogg, I found them to be first a hard transparent horny substance, without the least appearance of pores or holes in it; and this I try’d with the greatest care I was able, cutting many of them with a very sharp Razor, so that they appear’d, even in the Glass, to have a pretty smooth surface, but somewhat waved by the sawing to and fro of the Razor, as is visible in the end of the _Prismatical_ body A of the same Figure; and then making trials with causing the light to be cast on them all the various ways I could think of, that was likely to make the pores appear, if there had been any, I was not able to discover any. Next, the Figure of the Brisles was very various, neither perfectly round, nor sharp edg’d, but _Prismatical_, with divers sides, and round angles, as appears in the Figure A. The bending of them in any part where they before appear’d cleer, would all flaw them, and make them look white. The Mustacheos of a Cat (part of one of which is represented by the short _Cylinder_ B of the same Figure) seem’d to have, all of them that I observ’d, a large pith in the middle, like the pith of an Elder, whose texture was so close, that I was not able to discover the least sign of pores; and those parts which seem to be pores, as they appear’d in one position to the light, in another I could find a manifest reflection to be cast from them. This I instance in, to hint that it is not safe to conclude any thing to be positively this or that, though it appear never so plain and likely when look’d on with a _Microscope_ in one posture, before the same be examin’d by placing it in several other positions. And this I take to be the reason why many have believed and asserted the Hairs of a man’s head to be hollow, and like so many small pipes perforated from end to end. Now, though I grant that by an _Analogie_ one may suppose them so, and from the _Polonian_ disease one may believe them such, yet I think we have not the least encouragement to either from the _Microscope_, much less positively to assert them such. And perhaps the very essence of the _Plica Polonica_ may be the hairs growing hollow, and of an unnatural constitution.