As stated under PLUM, this is thought to be the original of all the cultivated European varieties of that fruit. The sloe is sometimes used as a hedge plant in Europe, and is planted

Sloe or Blackthorn (Prunus spinosa). around trees in parks to protect them while young from injury by animals; it is sometimes seen in this country in collections of shrubs, its chief merit as an ornament being its early flowering. The wood is hard, heavy, and darkcolored, takes a fine polish, and is used for handles to tools, flails, teeth to rakes, and the like; upright shoots make favorite walking sticks. The leaves when dried are regarded as more like tea than any other substitute; they were at one time largely collected for the adulteration of tea in England, but this is now forbidden under a heavy penalty. The fruit when mellowed by frost is eaten in some parts of Europe, and is made into a conserve; its expressed juice is used in Germany to mark clothing, it being nearly indelible, and in England it forms the basis of "British port."

SLOTH, the name of the edentate mammals of the family tardigrada (Ill.) and genus bradypus (Linn.); both the family and generic names are derived from the extreme slowness of the gait; it is le paresseux of the French. The skull is small, rounded, flat, and truncated in front; the jaws very short and the face very little projecting beyond the line of the cranium; the malar bone gives off a zygomatic process which runs backward and passes above the corresponding one of the temporal bone without touching it, a second process descending outside the lower jaw, which is very strong. The fore legs are much longer than the hind, and all the toes end in long curved claws, channelled underneath, the bones firmly united together and the claws naturally turned in against the soles; the fore feet have either three or two toes, and the hind feet three toes; the latter are articulated obliquely on the leg, so that only the exterior edge touches the ground, of course making progression on a level surface very awkward; the pelvis is so

wide and the thighs so laterally directed that the knees cannot be brought together. The ears are very short, and concealed under the hair, which is dry, harsh, and coarse. The axillary and iliac arteries, instead of pursuing their usual course down the limbs as single vessels, suddenly subdivide into from 40 to 60 small trunks of equal size, freely anastomosing with each other, looking somewhat like a mass of varicose veins, and distributed chiefly to the muscles; the arrest of the circulation by pressure on a single trunk is thus prevented, and its retardation permits slow and long continued contraction of the muscles of the arms and legs. The stomach is divided into four cavities without folds, the intestine is short, and the cæcum absent; the mammæ are two, and pectoral; there is a common cloaca, as in birds, for the expulsion of the urine and fæces. The dental formula is, the teeth being simple, separated, nearly cylindrical, without roots, with an undivided hollow base continually growing as they are worn by use, and composed of dentine and cement without enamel; there are no incisors; the anterior molars are very small in the three-toed sloth, but in the two-toed are long, pointed, resembling canines, and the lower placed behind the upper. The tail is very short, or absent. The sloths were considered by the early naturalists as imperfect and deformed creatures; but in the trees, their natural home, their peculiarities of structure are as admirably adapted for their convenience and enjoyment as in any other animal; the fore limbs have great freedom of motion, and all are so constructed that by means of the claws they suspend themselves to the branches and hang for a long time, and even sleep, back downward. They are rarely seen on the ground, for the reason that they can pass from one tree to another by the interlocking branches for miles in the thick forests of South America, which they inhabit from Guiana to Paraguay, some species extending to Peru, and according to some authors into Central America. They are rarely more than 2 ft. long, and their hair resembles in color the bark of the trees upon which they live; the food is entirely vegetable, the leaves and twigs of trees. They have one young one at a time, which clings to the mother's back, hiding among the hair; the native name is ai, from their feeble plaintive cry; they are remarkably tenacious of life, and apparently unconscious of pain.-Linnæus gave the name of B. tridactylus to a three-toed sloth, under the impression that there was only one species thus characterized, whereas Wagner describes several in the Archiv für Naturgeschichte for 1850. The animal referred to by Linnæus is grayish, with the body 14 in. long, the head about 3, the tail 1, the fore limb 11, the hind 6, and the claws 2 to 24; it has 9 cervical ver tebræ, and 14 ribs on each side, of which 9 are true; the thumb and little finger are rudimentary and hidden under the skin; there is a ru

dimentary clavicle attached to the acromion; the hair is reversed on the forearm. It has been calculated that it can take only 50 steps a day, consuming a month in traversing a mile;

Three-toed Sloth (Bradypus tridactylus).

if by chance it ascends a tree too remote from another to admit of a passage across, the natives say that it rolls itself in a ball and drops to the ground, and the thick wiry hair would render such a fall comparatively harmless; from its habits it can rarely if ever drink; its flesh and skin are useless; in captivity it is exceedingly stupid and uninteresting. The unau or two-toed sloth (B. didactylus, Linn.; genus

Unau or Two-toed Sloth (Bradypus didactylus). cholapus, Illig.) is mixed brown and white, paler below; it is about 2 ft. long, with, according to Daubenton, 23 ribs on each side, of which 12 are true; the clavicles are complete, and the tail is wanting: it has a longer muzzle and shorter fore legs than the three-toed species, and is more active, especially at night; it inhabits the same region, and is sometimes eaten by Indians and negroes.-For the fossil edentates, see MEGALONYX, MEGATHERIUM, and MYLODON; for anatomical details, see CoмPARATIVE ANATOMY, and EDENTATA.

SLOVAKS, a Slavic people, belonging to the western stem of the race, and inhabiting chiefly the mountainous regions of N. W. Hungary and the adjoining portions of Moravia. Their number is estimated at nearly 3,000,000, more than two thirds of whom are Catholics, and the remainder Lutherans. They are of medium stature, have blue eyes, straight and long hair, a yellowish skin, and generally coarse features. They are chiefly engaged in agriculture and mining. Numbers of them spend their lives wandering through various countries of Europe, selling linen, mouse traps, and other articles of wire work. The language of the Slovaks is a sub-dialect of the Bohemian or Czech, which latter is generally used by them as a literary medium, as by Kollar, Schafarik, Holly, and other writers, and is also the language of their church services.-The Slovaks occupied their present abodes early in the middle ages, and in the 9th century they formed the nucleus of the Moravian empire until its destruction by the Magyars.

SLOVENS, or Sloventzi. See WINDS.

SLUG (limax, Lam.), a genus of mollusks, belonging to the air-breathing gasteropods. The form is elongated, tapering, snail-like, the head having two long and two short tentacles which can be extended and drawn in like the finger of a glove by being turned inside and out; the naked body is covered anteriorly by a coriaceous mantle, under which is the branchial cavity, the respiratory orifice and vent opening on the right side of it, and the generative orifice beneath the right tentacles; the mantle in some contains a calcareous grit, and in others a small, thin, nail-like shell; the head can be partly drawn under the mantle; at the posterior end of the body is a small aperture whence proceed the adhesive threads by which they let themselves down from plants which they ascend in search of food. Their motion is proverbially slow, and effected by the contractions of the flat disk or foot on the ventral surface. The upper jaw is in the form of a toothed crescent, by which they gnaw plants with great voracity; the stomach is elongated; the skin secretes a great quantity of mucosity, which serves to attach them to the surfaces on which they creep; the eyes are small black disks at the end of the posterior tentacles; the sense of touch is delicate. The reproductive season is in spring and summer; they are hermaphrodite, and mutually impregnate each other; the eggs, to the number of 700 or 800, are laid in moist and shady places; at the approach of winter they burrow into the ground, where they hibernate; they hide under decaying logs and stones in damp places, and are seen in gardens and orchards in evening and early morning, especially after gentle and warm showers. They are found in the northern temperate zones of both hemispheres. The common slug of New England, L. tunicata (Gould), is nearly an inch long, varying in color from dark drab to blackish brown; the

back is wrinkled, and the upper tentacles granulated and black at the tips; the foot is very narrow; it is found almost always with the isopod crustaceans commonly called sow bugs. Other species are described; they are comparatively rare in the United States, and by no means so troublesome as in Europe. The common European slug, L. agrestis (Linn.), is small and unspotted, and very abundant and destruc

Slug (Limax agrestis).

tive; they are killed by solutions of tobacco, salt, or other irritants, or by covering a spot infested by them with ashes, lime, fine sand, or any powder which attaches itself to the body and prevents their walking, or they may be arrested by some sticky substance; many are devoured by mammals, birds, and reptiles. SLUG WORM, the common name of the larvæ of the sawflies, or the hymenopterous insects of the family tenthredinida. The slug worm described by Prof. Peck in his prize essay (Boston, 1799), and called by him tenthredo cerasi (Linn.), has been placed by Harris in the genus selandria (blennocampa). The fly is black, with the first pair of legs yellowish clay-colored; the body of the female is about a fifth of an inch long, that of the male a little smaller. They usually appear in Massachusetts on the cherry and plum trees toward the end of May, disappearing in three weeks after laying their eggs singly in incisions on the lower surface of the leaves; the young are hatched in two weeks, coming out from June 5 to July 20, according to season; they have 20 short legs, a pair under every segment except the fourth and the last, and are half an inch long when fully grown; in form they resemble small tadpoles, and are covered with a thick slimy matter which has given them the name of slugs; they also emit a disagreeable odor. They come to their full size in 26 days, casting their skin five times, after which they enter the ground, change to chrysalids, and come out flies in 16 days; they then lay eggs for a second brood, which enter the ground in autumn, and appear as flies in the ensuing spring, some remaining unchanged for a year longer. They feed on leaves, and in some seasons have been so numerous as to strip trees entirely of their foliage and even cause their destruction; they are eaten by small mammals and birds, and the

eggs are destroyed by the larvae of a tiny ichneumon fly (encyrtus). The trees may be best preserved against their attacks by showering them with a mixture of whale-oil soap and water, or powdering with ashes or quicklime. SMALCALD (Ger. Schmalkalden), a town of Prussia, in the province of Hesse-Nassau (before 1866 of Hesse-Cassel), 34 m. E. N. E. of Fulda; pop. in 1871, 5,792. It manufactures iron, steel, and salt.-The Smalcald league was concluded here in 1531, by various Protestant princes and free cities, for mutual defence of their religious and political independence against Charles V. and the Catholic states of the empire. It was limited at first to six years, but in 1535 new members were admitted at a second convention in Smalcald, and the term was extended ten years, with a resolution to maintain an army of 12,000 men. The elector John Frederick of Saxony and the landgrave Philip of Hesse became the leaders of the league, whose war against the emperor (1546-7) was terminated by the victory of the latter at Mühlberg, April 24, 1547. In 1537 a confession of faith was drawn up in several articles by Luther, known subsequently as the "Articles of Smalcald," which became one of the symbolical books of the Lutheran church.

SMALLPOX (variola), a contagious fever, characterized by a pustular eruption having a depressed centre. The terms variola and pacce first occur in the Bertinian chronicle of the date 961. Variola is derived from the Latin varus, a blotch or pimple, while pox is of Saxon origin and signifies a bag or pouch; the prefix small was added in the 15th century. The era commonly assigned for the first appearance of smallpox is A. D. 569; it seems then to have begun in Arabia, and the raising of the siege of Mecca by an Abyssinian army is attributed to the ravages made by smallpox among the troops. The new part which Arabia under Mohammed and his followers was made to play in history contributed to the rapid propagation of the disease throughout the world. Rhazes, an Arabian physician who practised at Bagdad about the beginning of the 10th century, is the first medical author whose writings have come down to us who treats expressly of the disease; he however quotes several of his predecessors, one of whom is believed to have flourished about the year of the Hegira, A. D. 622. Measles and scarlet fever were at first confounded with smallpox, or considered as varieties of it; and this error seems to have prevailed more or less until Sydenham finally showed the essential differences between them. Boerhaave was the first to insist that contagion is essential to the propagation of the disease.-The period of incubation, that is, the time that elapses from the moment the patient receives the contagion until it begins to manifest its effect in the initiatory fever, is usually 14 days, though it sometimes varies. During this time there is usually no disturbance of the ordinary health.