Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/689

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part where the crack begins, and immediately on its opening, the new flan is feen within, and loofe from it, and ia eafily known by the frefhnefs of its colours. As foon as the opening is once made, the creature eafily enlarges it, thrufting up its body, in part, out at the crack, and making it ferve in the office of a wedge, to enlarge and lengthen out the flit; by this means the creature foon extends the crack thro' four rings, and it has then a fpace large enough for it to draw out its whole body at. The firft efforts are made at the head, which, by feveral motions and turnings about, is at length made to be Ioofencd, and finally drawn wholly out of the old fkull, and elevated through the crack. This is then laid foftly upon the old fkin of that part, and the fame fort of motions in the tail end, difengaging that, in a little time it is alfo drawn out, and in the fame manner laid fmoothly and evenly upon the old ikin. As difficult as this laft operation may feem, it Is very fpeedily effected. It takes the animal indeed many days to prepare for it, but when the crack is once made in the Ikin, the whole remaining work is done in lefs than a minute. The beft method for obferving this amazing work, is by feeking out a neft of thofe caterpillars that live in communi- ties. Thefe are very common in gardens, and in the hedges j and, as many hundreds of them change their fkin in one day, it is eafy to be apprized of their being about it, by feeing the fkins hang upon the web ; and if they are watched, upon that fignal, the whole will be foon feen performed by feveral of them, often by many at a time. Reaumur's Hilt. Inf. vol. i. p. 229.

The hairs which _are found upon the caft fkins of the hairy caterpillars, fsem, at firft fight, to be like the other part o'f that Exuvia, only the cafes or coverings of thofe parts, in' the inclofed infect ; but, in reality, this is found not to Ifc the cafe in regard to them, whatever it be in all the others. Mr. Reaumur obferved three or four hairy caterpillars, at the time when they were juft preparing for their change ; and when they fhewed the very firft figns of its approaching, by ceafing to eat and move, he cut, with a fine pair of fctffars, many of the hairs off, as clofe to the body as he could. When the change was perfected, and this ikin thrown off, he examined the hairs of the parts, correfponding to thofe he had cut them fhort upon in the old fkin, while yet upon the ani- mal. If thefe had been the cafes of the new hairs, thofe muff, certainly have been cut fliort with them ; but, on the con- trary, they were found, in the caterpillar, as long in thofe parts as in any others. It appears from hence, that though all the other parts thrown offarebutthe fheathsand cafes to what they covered, yet the hairs are real and folid things them- felves; and hence it appears, that the creature, when hatched from the egg, muff have all its fkins perfectly formed, one lying under another, and each furnifhed with its covering of hairs, fo that the old ones are to fall off with the old fkins, and the new ones to appear with the new ; and probably thefe may be one great means of forcing off and diflodging the old ikin from every part, by the creature's erecting them in part. Reaumur's Hift. Inf. vol. 1. p. 241.

In making thefe hairs, however, fo great a means of getting off the fkin in the hairy caterpillars, we feem to leave the fmooth ones a much harder tafk to execute the fame operation without thefe afliftances ; but probably the fame fort of me- chanifm is ufed by all, and all are furnifhed with the fame fort of means to accomplifh it, tho' thefe are lefs obvious in fome than in others.

Many of thofe caterpillars which appear fmooth to the naked eye, are found to be really hairy, when examined by the microfcope ; and others are covered with a fort of little emi- nences or protuberances, which may very well ferve to the fame purpofes in diflodging the old fkin. When a nice diffection of the upper fkin is made longitudi- nally in the place where the crack is to happen for the animals getting out of its old fkin, and this is done in a caterpillar juft going to change, the fkin may be, with care, taken clean off, and the arrangement and difpofition of the hairs on the new fkin, while under cover of the old one, is eafily feen. The hairs on this are difpofed in the moft nice and artful manner imaginable, for their lying fmooth under the upper fkin. It is well known that thefe grow all in feparate tufts, and each of thefe tufts of hair are found difpofed in fuch directions, that they never lie upon one another, but together form one fur- face, fome being laid toward the back, others toward the belly, and fome in other lefs regular directions. Some cater- pillars have large tufts of hairs near their heads or tails, or both. 1 hefe refemble true feathers, and muft take up much more room under the fkin than the others, yet thefe, as well as the fingle hairs, are contained under the fkin ; for if thofe of the old fkin be cut off a few days before the change, the new ones will not be found mutilated by that means, but as long and perfect as if nothing had been done. And thefe alfo, on taking off the upper fkin, are feen laid in a beautiful order on the under one 3 in the animal, before the change of its fkin.

One thing very remarkable, in regard to this change of the fkin in thefe animals, is, that they always appear, immediately after their coming out of the old one, much larger than they Suppl. Vol. I,

EYE

M before. The thick tufts of hair on fome might feem to oc- cafion this appearance ; but it muft be a reality, fince it is an obfervation as old as Malpighi, that the very head and fkull are greatly larger, after this change, than they were imme- diately before. This, however, will be underftood, if we confider the operation of the crayfifh in changing its fhell. It in the fame manner is found to appear much larger, when out of the fkin, than before ; and this is, in both cafes, owing to this, that the body had grown fo much, that it was too big for its covering, which appears to be the principal reafon of its quitting it. While it remained in it, however, the parts were all compreffed together, and forced to lie in that narrow room, but as foon as the external covering, which occafioned that compreffion, is off, every part diftends itfelf to its proper hze, and the creature therefore appears much larger than it did before.

It is very certain, that fo large a fkull, being of a hard fub- ftance, in the caterpillar, could not have been compreffed into or contained in the fmaller, before the change : But the real fact is, that the new fkull never hardens till the change ap- proaches, and then but imperfeflly. It acquires, at that time, thro' neceffity, from the fhape of the place it lies in, an ob- long form ; and in this fhape is found, a few hours before the old fkin is caft off, not inclofed within it, but extending itfelf under the fkin of the firft ring of the body. When the old fkull is thrown off, with the fkin, the new one is as yet foft, and foon becomes of its proper rounded figure. Reaumur, Hift. Inf. vol. 1. p. 243.

EY, in our old writers, the fame with infula, an ifland ; from which comes eyet, a finall ifland or iflet, vulgarly called eyght.

EYE (Cycl.) — It is no uncommon thing for the Eyes to be terribly molefted by extraneous bodies, accidentally fallen into them, fuch as a bit of fand, a fplinter of wood, the cutting of a quill, or of one's nails, a finall infefl, or the like. The moft eafy method of getting thefe bodies out, is the opening and extending the eyelid with one's fingers, and agitating it, hold- ing the head down ; by this means the foreign bodies are often wafhed out of the Eye, by the encreafed flux of tears, without much difEculty. If this does not fucceeil, the beft method is next to blow fome levigated crabs-eyes, or the like fine pow- der, under the eyelid, that this, being wafhed out by the tears, may carry alfo the other bodies out with it. Hei/la's Surgery, p. 364.

If all this fails, the eyelid muft he gently and carefully lifted up, and the offending body fought for, and carefully taken out with the end of a probe, or the like inftrument. Or another method, is the dipping a fine pencil brufh, or a finall piece of ■ fpunge, tied to a finall ftick, into warm water, and pafling it under the eyelid, and by that means pufhing the offending matter out. Lime, or any other acrid fubftance, fhould al- ways be wafhed out with milk, or milk and water, and the Eye, after thefe accidents, be wafhed with a collyrium made of rofe water, with a little of the white of an egg beat up in it, and a finall admixture of faccharum faturni, or powder of tutty, and if there be any confiderable inflammation, it will be proper to bleed.

It is well known, from infpec\ion, and from the writings of anatomifts, that there are two veins which run one on each fide the nofe, thro' the canthi majorcs, or greater corners of the Eyes ; thefe proceed partly from the forehead, and partly from the Eyes, and, like the frontal vein, difcharge their blood down into the external jugular veins. Bleeding in thefe canthal veins has been approved of by all occulifts, for in- flammations, and other diforders of the Eyes, tho' perhaps with very little folid foundation. When this operation is to be performed, a ftricfure is made about the neck, and when the incifion has been made, the patient muft hold his head in a proper pofition for the blood to flow, without being trou- blefome to his Eye or mouth ; and when the neceflary quan- tity of blood has been difcharged, a thick triangular comprefs muft be applied, and fecured on, with a proper bandage. Heifter's Surgery, p. 282.

Running of the Mi us, ininfants. See Infant.

Scarification of the Eyes is a chirurgical operation, by many confounded with that of bleeding in the eyes, but improperly enough, fince the parts of the operation are different ; for bleeding is confined, in this organ, to the white of the eye alone, whereas fcarification is pra£tifed as well upon the inner furfacc of the eyelid, as on the white of the eye ; and they are alfo performed by different inftruments. This is no new operation, fince Hippocrates, Celfus, &c. all prefcribed it, but, of later ages, it grew much into difufe. To perform this operation, the patient is to be feated in a good light, and his head held ftill by an afliftant, while the furgeon prefles his thumb and forefinger on the eyelids, fo as to open them, and turn them outward, that their interior red furface may come into view, this is much more conveniently performed on the under than on the upper eyelid. When the furface is thus turned up, the furgeon draws the fcarifying in- ftrument backward and forward over it with great fwiftnefs, as alfo over the white of the Eye, if there be occafion, and, by this means, opens all the turgid veflels, and makes them 10 P bleed