METACHROSIS. 366 METAL TRADES ASSOCIATION. SEITIOS OF A FBOB's BKIK. caey, appearing wlu-ii dilated as species of metallic sheen. These changes may be due to the direct in- fluence of the stimulus of light, or indirectly through the eyesight. Semper says that Lister demonstrated as ^ long ago as 1858 that the activity of the chromato- phores depends solely on the healthy condition of the eye. As soon «. EpUlermi-s: d. cutis, with a^ the eyes are dc- black, star- shaped, d«'ii-Beat*d stroyed or the ojitic c<'lls ; r, (/, ypllow itifrinent cells in nerve is divi<le(l a thic]<, eiiiKie lawr close under ji i " * i ' the epidermis. thechroniatophon-s do not function. He was confirmed in this view by Pouchot's experi- ments on fishes and crabs, showing that the chroniatophores lost their power of contraction if the two sympathetic 'nerves were destroyed at the root. Heincke's observations in some respects contra- dict those of Pouchct. Biedemann (1802), on the other hand, has claimed that the color-cells change their shape owing to the direct action of the light and of temperature. He shows that the slightest change of tciiiperature affects the mu- tual disposition of the pigment-cells, and conse- quentlv the color, of the frog. It is enough to keep the animal in the hand to provoke a con- traction of its black cells. The amount of hlood- supply also has a definite eflfect. Steinach also (18!)1) has proved that light acts as a direct stimulus. Biedemann therefore appears to have proved that the chief agency of changes of color is not in the sensations derived from the eyes, but in those derived from the skin. It is well known that the under side of flatfish is white or colorless. This is due to absence there of pigment-cells. These, however, are present in very young flounders, but as they grow unsymnielrical the fish turns the left side up- ward, and the chroniatophores disappear from the right or under side. Ciinninghan) experi- menti'd with young flounders liy ])lacing a mir- ror below the aquarium at an angle of 4.5°. and cut off the light from above. In the larger nuni- lier of specimens thus treated, after several months, more or less of the .skin of the lower side was pigmented. He thus proved that the absence of pigment on that side in the normal fish is due to its position in shadow. It thus appears that the absence of the pigment or of color is due to the absence of light, a mechanical or physical cause. Binr.ior.nAPHV. Semper. Animal Life as Af- fected hji the Xnttiral Con/iilions of Existence (New York, 1881) : Biedemann, "Ueber den Far- benwechsel der Friische," in Arehiv fiir die (je- samnitc Phimiotoijie. vol. li. (Bonn. 1802) ; Gadow, Amphibia and Reptiles (London and New Y..rk. 10(1-2). MET AGEN'ESIS. See Alternation of GeNKK A I MiS ; I'aUTIIKNOOEXESIS. MET'AKINE'SIS (Gk. /teTaiilvi/aic. trans- position, from fieraxivtiv, metakincin, to trans- pose, from /ifrii, meta, after -|- Kivelv, Jcincin, to move). A term suggested by .Jaekel to ex- press the results of cenogenetie modification. since the process involves a thoroughgoing modi- fication of a form in a way impossible in the adult, and only possible in a larval or early stage, in which the various organs are not yet specialized and are still more or less plastic. Consult Jaekel, Ueber i-erseliiedeiie wcge phi/lo- (jenetischer Eutunckelung (.Tena, 1902; reviewed in Science, vol. xvii. p. 380, Xew York, 1903). Compare Palikgexesis. METAL. In heraldry, one of the three classes of tiiuturi's, the others being colors and furs. See IlEiiALimv. METAL-CASTING. See Foixdi.ng. METAL'DEHYDE. See Aldehyde. METALLIC PAINT. See :Mjxebal Paint. METALLURGY (from Gk. fi£ra/,?.o.'/j>(}(, nui(ill()urg(js, metal-working, from tuTtt'/J.ov, met- allon. metal, mine + ipyov, eryon, work). That branch of applied science which has for its ob- ject the preparation of metals from their ores. The ojjerations of metallurgy- are partly mechani- cal and partly chemical. The mechanical opera- tions of metallurgy- are fully described under ; Ore DKE.S.SI.NG, and the chemical operations, which differ in detail for each metal, are de- : scrilied in the articles on the various nietnU. Briefly stated, ore dressing consists in separating . the valuable ore or mineral from some of the barren rock with which it is mixed upon coming from the mines and in otherwise rendering it by mechanical means, such as crushing, sorting, anil washing, better fitted for the smelting or other operations of extraction which follow. The proc- esses of extraction may be separated into; (1) Smelting processes, in which the metal is extracted from its ore by fire; (2) amalgaiiiatinn jirocesses, in which the metal forms an amalgam with mer- cury, the mercury being afterwards distilled off, leaving the metal: (3) extraction by aqueous solutiims, in which the metal is dissolved by suit- able chemical solutions and then precipitated in solid form by suitable precipitants; (4) elec- trolytic processes, in which the metal is separated from its impurities by electrolysis. Two or more of these processes are often combined in the metallurgy of a single metal. See Al.l'MlxifM; Coi'i'F.R; (Jold: Iro.n and Steel; Lead: Xkkel; I'l.ATixrM: ^Ifrciry: Sh.vkr; Tin; Zinc; etc, METALS AND METALLOIDS. Sec Pebi- (iiuc Law. METAL TRADES ASSOCIATION, TliE N.rio.'AL. An association compii>cMl of about 200 firms in the metal trades, organized in -Au- gust, 1800, for the puriiose of resisting what the association regards as the excessive demands of labor organizations. The declaration of prin- ciples disavows "any intention to interfere with the proper functions of labor organizations," an- nounces that "no discrimination will lie made against any man because of his membership in any society or organization." indcuses arbitrn- tion. but asserts that the fiilhnving qiiestiniH must be decided by the employer alone; (1) the selection or rejection of workmen for the per- formance of particular tasks; (2) the number of apprentices, helpers, and handy men to be employed; (3) the method of wage payment, whether by time, piece, contract, or premiuBI rate. The association further declares that it* members will not arbitrate any question after cmplnyees have gone on a strike: neither will the association countenance a lockout on any arbi- trable question, unless arbitration has failed.
