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LEFT METAL-WORKING MACHINERY 203 METCHNIKOFF ruthenium, rhodium, osmium. (Several of the rare metals are here omitted.) See Mineral Production, United States. METAL-WORKING MACHINERY, machines and devices for the shaping of raw metals into the finished forms re- quired by commei'ce, or the engineer's designs. There are two main classes: First, those machines which make or per- fect one article or design in great num- bers, and with speed, and, second, those which are adapted to all kinds of work. The latter are called machine tools, and are controlled by the workmen, where- as the first class are usually to a large extent automatic. METAMORPHIC ROCKS, or META- MORPHIC STRATA, in geology, the term — first proposed by Lyell in 1833, and since universally adopted — for the stratified crystalline rocks — that is, rocks •which have been presumably laid down originally by the action of water, and then transformed by fire, chemical agency, pressure, or all combined. Meta- morphic action is divided into local — af- fecting only small portions of rock, or small areas, and regional — affecting rocks over considerable regions. The metamorphic rocks constitute one of the five great classes of rocks. The chief are gneiss, eurite, hornblende schist, serpen- tine, actinolite schist, mica-schist or micaceous schist, clay slate, argillaceous schist or argillite, chlorite schist, quartz- ite or quartz rock, and crystalline or metamorphic limestone. Besides these which were probably the first sedimen- tary, the other classes of rocks have in places undergone metamoi*phosis. METAMORPHOSIS (-mor'f o-sis), a change or transformation in the form, shape, structure, or character of any- thing. In botany, a change, especially of an abnormal character, in an organ. It may be progressive or retrogressive. Caljrx, corolla, stamens, and pistils are all trans- formed leaves. In entomology, it means a series of transformations which insects undergo in their progress from the egg to full maturity. There are analogous changes that are more or less complete in the other orders. In zoology, metamorphosis takes place in many other animals besides insects. Thus a barnacle (Lepas) or an acorn- shell (Balanus) is at first a free and swimming creature, which ultimately be- comes sedentary and attached to rocks or ships' bottoms. Metamorphosis ^ exists also in Annelids, in Mollusks, in Me- dusas, etc. METAPHOR, a figure of speech in which one object is likened to another by speaking of it as if it were that other; distinguished from a simile by not em- ploying any word of comparison, such as "like" or "as." METAPHYSICS, a term popularly employed to denote a science dealing with subjects incapable of being dealt with by physical research. METAURUS (-ta'-), a river of central Italy, still called the Metauro, emptying into the Adriatic near Fano. On its banks the Romans defeated the Cartha- ginians under Hasdrubal in 207 B. C. METAYER (-ta'yur), one who culti- vates the soil under an arrangement with his landlord, not paying a fixed rent, either in money or in kind, but a certain proportion of the produce, the landlord furnishing the whole or part of the stock, tools, etc. METAZOA (-zo'-), many-celled ani- mals, composed of tissues, originally developed from three cell^ layers. The group comprises all the higher animals, from sponges to man, and is opposed to the Protozoa?, which are microscopic or one-celled animals. METCALF, VICTOR HOWARD. American public official; bom at Utica, N. Y., Oct. 10, 1853. He was graduated from Yale in 1876, and was admitted to the Connecticut and New York bars in 1877, after which he practiced at Utica, and Oakland, Cal. In 1899 he was elected as Republican member to Con- gress from California. In 1904 he was appointed by President Roosevelt Secre- tary of the Department of Commerce and Labor, and in 1906 Secretary of the Navy, retiring in 1908 on President Taft's election. METCHNIKOFF, ELIE, a Russian bacteriologist, born in Kharkov, Russia, 1845. He studied in Germany, then be- came professor of zoology at Odessa in 1870. In 1882 he devoted himself _ ex- clusively to private research, especially devoting himself to the digestive func- tions in animal organisms. Later he set- tled in Pai-is and was made chef de ser- vice in the Pasteur Institute in 1892. He was especially known for his theory on dieting, to the effect that old age rnay be retarded by refraining from eating certain foods which tend toward auto- intoxication. In 1908 he shared with Pro- fessor Ehrlich the Nobel prize for medi- cine. In 1909 he advanced his theory that a certain kind of soured milk con- tained bacilli, counteracting or retarding autointoxication. He died in Paris in 1916.