Micrographia - or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon/Chapter 26
Observ. XXVI. Of Cowage, and the itching operation of some bodies.
HTere is a certain Down of a Plant, brought from the East-Indies, call'd commonly, though very improperly, Cow-itch, the reason of which mistake is manifest enough from the description of it, which Mr. Parkinson sets down in his Herbal, Tribe XI. Chap. 2. Phasiolus siliqua hirsuta; The hairy Kidney-bean, called in Zurratte where it grows, Couhage: We have had (says he) another of this kind brought us out of the East-Indies, which being planted was in shew like the former, but came not to perfection, the unkindly season not suffering it to shew the flower; but of the Cods that were brought, some were smaller, shorter, and rounder then the Garden kind; others much longer, and many growing together, as it were in clusters, and cover'd all over with a brown short hairiness, so fine, that if any of it be rubb'd, or fall on the back of ones hand, or other tender parts of the skin, it will cause a kind of itching, but not strong, nor long induring, but passing quickly away, without either danger or harm; the Beans were smaller then ordinary, and of a black shining colour.
Having one of these Cods given me by a Sea-Captain, who had frequented those parts, I found it to be a small Cod, about three Inches long, much like a short Cod of French Beans, which had six Beans in it, the whole surface of it was cover'd over with a very thick and shining brown Down or Hair, which was very fine, and for its bigness stiff; taking some of this Down, and rubbing it on the back of my hand, I found very little or no trouble, only I was sensible that several of these little downy parts with rubbing did penetrate, and were sunk, or stuck pretty deep into my skin. After I had thus rubb'd it for a pretty while, I felt very little or no pain, in so much that I doubted, whether it were the true Couhage; but whil'st I was considering; I found the Down begin to make my hand itch, and in some places to smart again, much like the stinging of a Flea or Gnat, and this continued a pretty while, so that by degrees I found my skin to be swell'd with little red pustules, and to look as if it had been itchie. But suffering it without rubbing or scratching, the itching tickling pain quickly grew languid, and within an hour I felt nothing at all, and the little protuberancies were vanish'd.
The cause of which odd Phænomenon, I suppose to be much the same with that of the stinging of a Nettle, for by the Microscope, I discover'd this Down to consist of a multitude of small and slender conical bodies, much resembling Needles or Bodkins, such as are represented by A B. C D. E F. of the first Figure of the XVI. Scheme; that their ends A A A, were very sharp, and the substance of them stiff and hard, much like the substance of several kinds of Thorns and crooks growing on Trees. And though they appear'd very cleer and transparent, yet I could not perceive whether they were hollow or not, but to me they appear'd like solid transparent bodies, without any cavity in them; whether, though they might not be a kind of Cane, fill'd with some transparent liquor which was hardned (because the Cod which I had was very dry) I was not able to examine.
Now, being such stiff, sharp bodies, it is easie to conceive, how with rubbing they might easily be thrust into the tender parts of the skin, and there, by reason of their exceeding fineness and driness, not create any considerable trouble or pain, till by remaining in those places moistned with the humours of the body, some caustick part sticking on them, or residing within them might be dissolv'd and mix'd with the ambient juices of that place, and thereby those fibres and tender parts adjoyning become affected, and as it were corroded by it; whence, while that action lasts, the pains created are pretty sharp and pungent, though small, which is the essential property of an itching one.
That the pain also caused by the stinging of a Flea, a Gnat, a Flie, a Wasp, and the like, proceeds much from the very same cause, I elsewhere in their proper places endeavour to manifest. The stinging also of shred Hors-hair, which in meriment is often strew'd between the sheets of a Bed, seems to proceed from the same cause.