Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/98

 MUS

they appear. Thefe fpots appear bell by looking at diftant bright objects, and are always of the fame colour with the object. In the middle their colour is clear and ftrong, fur- rounded by a dark fhady border. They are commonly ac- companied with certain irregular veins, which proceed from each fpot, and which as well as the fpots themfelyes change their order and difpofition. Thefe veins are alfo of the fame colour with the object, and being bright and luminous in the middle, are likewife terminated by a dark and obfeure edge. Thefe fpots change their pofition with refpect to the axes of vifion, according as the eye is differently moved, being fome- times in the axis of vifion itfelf, and at other times to the right or left of this fame axis ; but when the eye is kept fixed in the fame direction, they, as well as the dark kind of fpots firft mentioned, commonly defcend gradually. As to the caufe of thefe brighter fpots and veins, it feems that, firft, they muft proceed from fome corpufcles within the eye, which are at liberty to change their place, and which there- fore muft be fuppofed to float in the aqueous humor. Second- ly, feeing thefe fpots always defcend when the eye is kept fix- ed, the corpufcles from which they arife muft afcend ; and are confequently lighter than the aqueous humor in which they fwim. Thirdly, thefe fpots being more bright and lu- minous than the 'object, they cannot be occafioned by any opaque corpufcles, which by intercepting the rays would caft a ftiade upon the retina. What therefore bids faireft tor pro- ducing thefe brighter fpots and veins, is fome fmall, oily, diaphanous particles and filaments which fwim in the aqueous humor before the cryftalline ; for fuch, by their lightnefs, will afcend, when left to themfelves ; and by their greater refrac- tive power, produce thefe luminous fpots terminated by dark lines. That oily and fulphureous fubftances, though lefs denfe than water, have a ftronger refractive power, is evident from the obfervations of Sir Ifaac Newton. From which it follows, that the rays of light, which pafs through thefe oily particles, will meet fooner behind the cryftalline, than the other rays. Whence in a prefbytical eye, the rays of light which come from the feveral points of the object will nut converge to fo many other points in the retina, but behind it, by which the picture in the retina, will be rendered more dark and obfeure ; but the rays which pafs through thefe oily grains, by having their refraction increafed, will meet nearly at the retina, where they will form fmall luminous fpots, furrounded with dark borders.

But we muft here obferve, that the fame appearances happen to myopes ; and this feems difficult to account for from this theory of the learned doctor.

Many medical authors have looked on the Mufcte volitantes as forerunners of a cataract, or gutta ferena. And we fuppofe it cannot be denied, that many who have fallen into thofe ter- rible diforders have had thofe appearances before their eyes j and hence they might have been taken for prognoftics. But as it is no lefs certain, that many thoufands have the fame appearances, and yet preferve their light very well to the Jaft, there feems to be no great reafon to be alarmed about them ; and far lefs fhould people be running to quacks, and injuring their ftomachs and constitutions by ill-judged phyfic on fuch occafions. St. Yves denies thefe appearances to be at all dangerous, and he thinks them owing to the fcparation of fome parts of the retina from the choroid. However, as the diforder is troublefome and alarming to the patient, he advifes purgatives from time to time, and millepedes. We can fay, from experience, that neither mercurials, nor fea-water, nor other purgatives, nor millipedes, nor again Tunbridge or o- ther chalybeate waters, have had any effect towards removing or diminifhing thefe diforders. A greater dofe of wine than ufual has been known to increafc it for a little time ; and Plempius has made the like obfervation. We fhall only add, that feveral of thefe flying appearances refemble little glo- bules joined by threads, thus

and thefe globules appear in different numbers, and at different cfiftances.

All authors agree, that thefe appearances change their figure ; which is true, in fome meafure ; but from our own obferva- tion we can fay, that though they feem on a fudden looking to the fky, or other bright object, to vary in their figures ; yet when they begin to defcend, they return in one conftant fi- gure before we lofe fight of them. On the whole it feems, this phenomenon is not yet fully accounted for. The vafcu- lar form of mod of thefe appearances, their refemblances to fmall veins or arteries, makes it difficult to conceive them floating in the humors of the eye j and, on the other hand, their feeming contortions, and change of figure on fuddenly looking up, or making the head, makes it no lefs difficult to conceive them fixed and obftructed capillaries, as many au- thors fuppofe. MUSCARJ, in botany, the name of a genus of plants ; the characters of which are thefe : The flower is liliaceous, but confitts only of one leaf, of a fomewhat globular form, and divided into fix fegments at the edge ; the piftil arifes from the bottom of the flower, and finally becomes a fruit of a fort of triangular form, which is divided within into three cells, and ufually contains a number of roundifh feeds.

MUS

The fpecies of Mufcari, enumerated by Mr. Tournefort, are, thefe: i. The purple -flowered broad-leaved field Mujcari^ called by authors the great purple boytroide or fair- haired hyacinth. 2. The broad-leaved field Mufcari,- with white flowers. 3. The great blue-flowered Mujcari. 4. The broad-leaved elegant Mufcari, 5. The great white-flowered Mujcari. 6. The Mufcari with bluifh green flowers. 7. The white-flowered byzantine Mufcari. 8. The branched Mujcari. g. The fmaller branched Mujcari. 10. The frnaller broad -leaved blue-flowered Mufcari. n. The leffer rufhy-leaved blue field Mufcari. 12. The leffer flefh- coloured flowered rufh-Ieaved field Mufcari. 1 3. The little rufhy-leaved field Mujcari^ with white flowers. 14. The perfumed Muf- cari, with a dark greyifli flower. 15. The fweet-fcented Mufcari, with a brownifh flower. 16. The black ifh-flower- ed Mujcari* 17. The yellow-flowered Mufcari. 18. The early yellow- flowered Mufcari. Tourn. lnft. p. 347. feq. We have feveral fpecies of this plant cultivated in gardens ; Three or four for the beauty of their flowers, and one with a purplifh green flower for the remarkable fweetnefs of its fcent. In June, when the leaves of thefe plants are decayed, the roots fhould be taken up, and fpread upon mats in a dry place for a fortnight, till the bulbs are dried ; then they may be packed up, each fort by itfelf, till October, when they are to be plant- ed in borders for flowering the following fpring. They ini,uld never be fuffered to remain in the ground more than two years unremoved j for they multiply lo fait that the number of the off-fets greatly weakens the flowering roots, and the flowers are confequently fmall. They are eaiily propagated by thefe off-fets, which are fo hardy as to grow even if buried a foot under ground ; and the common kind propagates itlelf fo faft this way, that when it has once got poileJlion of a bed it is with great difficulty extirpated. Miller's Gardener's Diet.

MUSCERDA, a name by which fome authors have called moufe-dung, a thing recommended by many as a purge for infants ; and faid to be good in alopecias. Given in clyfters it is faid to be of fervice in many diforders of the bowels ; and externally applied, to be of great ufe in condylomata of the anus.

MUSCICAPA, in zoology, a name by which Aldrovand and fome others have called the ji one- chatter ■> making that bird, which is properly an cenanthe, one of the fpecies of that genus or the fly-catchers. Aldrovand de Avid. See the article Stone-chatter.

Muscicapa, the Fly-Catcher, is alfo the name of a fmall bird of the ficedula kind, and very nearly allied to the bec- cifago, or petty-chaps. It is called alfo in fome places, chivin and borin. It is a little larger than the wren, and has a very fharp- pointed beak. Its head, neck, and back are of a pale grey, and its throat and belly of a yellowifh white. Its rump is white; its wings grey; its tail, feet, and legs, are brown 5 and its claws very flendc. Ray's Ornithulogy, p. 158.

MUSCLE [Cycl] — Mr. Winflow, in his treatife on the Muf- cles in his Expojition anatomiaue de la Structure du Corps hu- main, fhews prodigious varieties in the actions of thefe organs of motion, which were never fo much as hinted at before. Dr. Waltherus, after comparing the Mufcles of the human body with the defcriptions of them publifhed by feveral au- thors, particularly by Mr, Winflow, has made feveral ac- curate remarks on them, which may ferve as a fupplement to his Anatome teneriorum Mufculorum repetita. Nov. Act. Erud. June 1733.

The Mujcks in fifhes are not placed lancellatim, or one upon another in a longitudinal direction ; but they are generally laid either tranfverfely or fomewhat obliquely one behind another, from the anterior part of the body to the origin of the tail. This ftructure is belt feen in the fpinofe fifhes. ThefeMufcles of the fpinofe fillies may be conveniently divided according to their fituation into the dorfal, pectoral, and neu- tral. After thefe, the inferior ones of that part of the body near the tail, are to have their place ; and finally, the cepha- lic, or thofe of the parts about the head.

The dorfal Mufcles have an interftice in the middle of the length of the back, or are feparated longitudinally from one another, and are terminated in the fides over-againit the fpina dorfalis. The pectoral and ventral Mujcks take their origin from the bafis of the ribs, and they meet in the middle of the breaft and belly. The Mufcles of the lower part of the body arife along the fpina dorfi, and meet one another in the bot- tom of the belly. The cephalic Mufcles ferve to the moving the eyes and the jaws, and are principally four : one is placed on each fide under the eyes, and one on each fide in the lower jaw. The two former are called the hypophthalmic Mujcles, and the two others the maxillary Mufcles x, they are moft evi- dent in the gadi, £5V.

Muscles of Vegetables. The Mufcles in animal bodies have been the fubject of numerous diilertations ; but thofe in ve- getables have been lefs regarded. Mr. Tournefort, however, has plainly proved, that many of the veifels of plants become in the drying fibres capable of tenfion ; that in many plants there are great numbers of thefe fibres which have all tbe fame direction, and always act all together, and can only 7 fhorten