RAT 435 RATEL hernia (where it is said to extend to the Upper Silurian), in Saxony, etc. RAT, in zoology, a name popularly applied to the lai'ger murines, but more strictly applicable to two species, the English black rat (Mus rattiis) , and the brown, or Norway rat (M. deeumanus) . The former is a small, lightly built animal, about seven inches long, with a slender head, large ears, and a thin scaly tail longer than the body. In tem- perate climates the color is a bluish- black lighter on the belly. The species is represented in warmer climates bj^ the Alexandrian rat {M. alexandrinus, better known as M. rattus 't'ufescens) , with a gray or reddish back, and white AUSTRALIAN KANGAROO RAT under -surface. By later naturalists it is considered as only a variety. The albino and pied rats, kept as pets, also belong to this species, which had its home in India and penetrated thence to almost every part of the world, driving out the native rats, and to be, in its turn exter- minated by the brown rat (probably a native of China, where a similar spe- cies, M. humiliatus, is still found). The brown rat is much more heavily built than the black rat, grayish-brown above and white beneath; ears, feet, and tail flesh-colored. Melanism often occurs, but such animals may be readily dis- tinguished by ordinary specific differ- ences from the true black rat. Length of head and body eight or nine inches long, tail shorter. Both the species are omnivorous, predaceous, and extremely fecund, breeding four or five times in the year, the female producing from 4 to 10 blind, naked young, which breed in their turn at about six months old. M. fuscipes is the brown-footed rat of Australia; Nesokia hmidicota, the bandicoot, or pig rat; and N. bengalen- sis, the Indian field rat. Figuratively: (1) One who deserts his party (espe- cially in politics), as rats are said to forsake a falling house or a doomed ship. (2) A workman who takes work for less than the regular wages current in the trade; also a workman who takes employment at an establishment where the regular hands have struck; a term of opprobrium applied to non-union men by members of trades unions ; specifically to non-union printers. RATA (Metrosideros robusta) , a New Zealand tree related to various species of ironwood. The seed is believed to be swallowed by a caterpillar, and to sprout in its interior, the fostering grub being of course killed. The tree begins life as a climber, attached to other forest trees, and attains a height of 150 feet; but when it has killed the supporting stem the rata is able to sustain its own weight and to grow on as an independent tree, attaining ultimately a height of nearly 200 feet. The wood is very hard, formerly much used for making clubs, and is valuable for shipbuilding. RAT-BITE FEVER, an infection aris- ing probably from a spirochete, present in the blood of about 3 per cent, of house rats, and consequently called spirochaeta morsusmuris by Japanese specialists. The spirochetal theory is supported by the efficacy in the fever of salvarsan, which is known to have a remedial effect in spirochete cases. RATCHET, in machinery, the detent which prevents the backward motion of a racket wheel. RATCHET WHEEL, a wheel having inclined teeth for receiving a ratchet or detent, by which motion is imparted or arrested. The teeth are of such shape as to revolve and pass the detent in one direction only. The detent may be a pallet or a pawl. The former receives an intermittent rotation by a reciprocat- ing circular movement of the arbor and its cam. Sometimes the wheel is int^- mittingly rotated by the motion of one pawl, while the other one acts as a de- tent in the intervals between the for- ward motions of the former. RATCHET WRENCH, a wrench oper- ated by a ratchet and pawl, so that it may be turned continuously without re- moval from the bolt or nut to which it is applied, by a backward and forward movement of the handle. RATCHMENT, in architecture, a kind of flying buttress which springs from the principals of a herse, and meets against the central or chief principal. RATEL, the genus MelUvora. Two species are usually distinguished, M, indica, the Indian, and M. rate!, the Cape ratel. The body is stout and heavily.
