| 释义 |
▪ I. lac1|læk|
Forms: α. (6 lacha, lacta), 6–9 lacca, (7 lacka, 8 laca, lakka). β. 6–8 lack(e, (7 lache, 7–8 lacque, 8 lacc, 8–9 laque), 7– lac.
[ad. Hindustani lākh:—Prakrit lakkha:—Skr. lākshā, also rākshā. Cf. F. laque, Pr., Sp. laca, It. lacca.]
1. (Also gum-lac.) The dark-red resinous incrustation produced on certain trees by the puncture of an insect (Coccus or Carteria lacca). It is used in the East as a scarlet dye. The incrusted twigs are called stick-lac; the resin broken off the twigs and triturated with water to remove the colour is called seed-lac; melted, strained, and formed into irregular thin plates, it is known as shell-lac or shellac n.
α1553Eden Treat. Newe Ind. (Arb.) 21 marg., Lacha, Lacca, or Lacta, is ye gumme of a tree wherewith silke is colored. 1622–62Heylin Cosmogr. iii. (1682) 217 Lacca (a gum there made by Ants, as here Bees make Wax). 1693Phil. Trans. XVII. 934 Manna and Gum Lacca he clearly shews to be Spontaneous Exudations. 1753Chambers Cycl. Supp. s.v. Lacca, A tincture of gum lacc may be thus prepared. 1763W. Lewis Comm. Phil. Techn. 223 Lacca..is found incrustated on sticks or branches of trees. 1809Wilford in Asiat. Researches IX. 65 This Amber of Ctesias is obviously the Indian Lacca, which has many properties of the Amber.
β1618T. Barker in St. Papers Col., E. Indies 1617–21 (1870) 159 Saffron, gumlac, indigo, copper. 1662J. Davies tr. Mandelslo's Trav. ii. (1669) 122 At Bantam..they sell store of Lacque, whereof they make Spanish wax. 1698Phil. Trans. XX. 273 Gum Lack is the House of a large sort of Ants, which they make on the Boughs of Trees. 1727Bradley Fam. Dict. s.v. Gum, Powder of Oister-shells, or Gum Lacque in Powder. 1794Pearson in Phil. Trans. LXXXIV. 385 White lac, in its dry state, has a saltish and bitterish taste. 1838T. Thomson Chem. Org. Bodies 550 Lac..is deposited in different species of trees in the East Indies, namely, the ficus indica, ficus religiosa, and rhamnus jujuba. 1877C. W. Thomson Voy. Challenger I. i. 15 The different varnishes and lacs remain soft and sticky.
†2. The colour of lac; crimson. Also, a pigment prepared from lac. Obs. (Cf. lake n.6)
1677Grew Colours Plants iii. §13 Spirit of Sulphur on a Tincture of Violets turns it from Blew to a true Lacke, or midle Crimson. 1689Marvell Instr. to Painter 636 Scarce can burnt iv'ry feign a hair so black, Or face so red, thine ocher and thy lack. 1763Brit. Mag. IV. 659 There are three sorts of lacque: the fine Venice lacque, the Columbine lacque, and the Liquid lacque.
†b. An extractive pigment; = lake n.6 3.
1682Weekly Memorials 27 Mar. 74 He also teaches us a way of preparing a sort of Lacca, or Paint, out of every Flower, by which it may be drawn or pictur'd in its own..Native Colour.
†3. The varnish made from lac; also applied to various resinous varnishes used for coating wood, etc.; = lacquer 2 a, 2 b.
1598W. Phillips tr. Linschoten i. lxviii. 117 Desks, Targets, Tables [etc.]..that are all couered and wrought with Lac of all colours and fashions. 1669Phil. Trans. IV. 985 No Arts are to be met amongst them, that are not known in Europe, except that of making Lacca. 1697W. Dampier Voy. (1729) II. i. 24 The Lack with which Cabinets and other fine Things are overlaid. 1727A. Hamilton New Acc. E. Indies I. ii. 126 The Lack is clear enough, but always clammy.
4. Ware coated with lac or lacquer.
1662J. Davies tr. Mandelslo's Trav. i. (1669) 24 Boxes of Lacque or Silver. 1861C. P. Hodgson Resid. in Japan 28 By degrees, the eye becomes accustomed to old laque..Old laque is, like old lace, inimitable. 1888Pall Mall G. 11 Feb. 3/1 The gems of Mr. S.'s unrivalled collection are here to show the supreme masterpieces in ‘lac’.
5. attrib., as lac-panel, lac-resin, lac-tree, lac-varnish; lac-cochineal, the insect that produces lac (Coccus lacca); lac-dye, a scarlet dye prepared in India from lac; lac-lake, the purple or scarlet pigment obtained from lac.
1813Bingley Anim. Biog. III. 191 The *lac cochineal.
1846Pope's Jrnl. Trade p. xxxi, Cochineal, Indigo, *Lac⁓dye. 1883Cassell's Fam. Mag. Oct. 683/1 Comparatively few people know how the lac-dye they read of in commerce is produced.
1895Daily News 24 May 6/6 A gold box..with old *lac panels.
1876Preece & Sivewright Telegraphy 296 The *gum lac resin is employed to consolidate the carbon⁓peroxide of manganese mixture.
1763W. Lewis Comm. Phil. Techn. 331 The species, called by Mr. Miller the true *lac tree, was found to contain, in its bark..a somewhat milky juice.
1688G. Parker & J. Stalker Japaning 1 The other [strainer] for your *Lacc-varnish. 1799G. Smith Laboratory I. 178 Make a paste of chalk and lack varnish.
Hence † lac v. trans., to cover or varnish with ‘lac’; to lacquer.
1698Phil. Trans. XX. 275 And then with a Brush [they] lay it smooth on any thing they design to Lack. 1727A. Hamilton New Acc. E. Indies I. xi. 125 They make fine Cabinets, both lack'd and inlaid with Ivory. Ibid. 126 They lack wooden Dishes and Tables, but not so well as in China.
▪ II. lac2 Biol.|læk|
An abbrev. of lactose used (usu. attrib.) as a symbol or name (and printed in italics): orig. used to denote the ability (of normal individuals) or inability (of mutants) of the bacterium Escherichia coli to metabolize lactose (see quot. 1947), and later to designate (the parts of) the genetic system involved in this ability; as lac operon, a group of adjacent genes in the chromosome of E. coli which, in the presence of lactose, cause the bacterium to synthesize the enzymes that enable it to metabolize lactose. Also as n., the (in)ability to metabolize lactose; a lac+ bacterium; the lac operon.
1947J. Lederberg in Genetics XXXII. 505 Particular attention was paid to the isolation of ‘lactose-negative’ or ‘Lac-’ mutants [of E. coli]. Ibid. 506 (Table), Symbols used for various loci... ‘Sugar’ fermentation. The ability to ferment is designated ‘+’; the inability ‘-’. Lac lactose. Gly glycerol. 1952Nature 24 May 882/2 The number of papillæ forming on surface colonies of lac- bacteria, grown on agar containing lactose and another carbon source, is a reflexion of the number of mutations to the lac+ condition. 1961Sager & Ryan Cell Heredity v. 136 If a cell [of E. coli] heterozygous for lac+ and lac - is isolated, it produces some progeny still heterozygous and others in which the lac- has segregated from the lac+. 1961Jacob & Monod in Cold Spring Harbor Symp. Quant. Biol. XXVI. 197 (caption) Genetic map of the Lac region of E. coli... The lower line represents an enlargement of the Lac region, with the two structural genes z and y and the regulator gene i. 1961S. E. Luria in Ibid. 210/1 An altered sensitivity of phage-carried lac genes to the specific repressor of the lac operon. 1970J. R. Beckwith in Beckwith & Zipser Lactose Operon ii. 5 (heading) Lac: the genetic system. Ibid., Strains in which the lac genes are fused to other bacterial operons, such as the trp operon and purE operon... Since, in such strains, the lac genes are now part of the other operon, nearly all the methodology used for analysis of lac can be used for that operon. Ibid., Most of the major concepts of operon structure, expression and regulation have come out of the work on the lac operon of E. coli. 1971Times Lit. Suppl. 13 Aug. 958/4 Dr Beckwith..[is] the centre of a political storm-in-a-scientific-teacup following his isolation of the lac operon gene.
▪ III. lac
obs. form of lack n.1 and v.1; var. lakh. |