| 释义 |
parasitic, a. and n. pl.|pærəˈsɪtɪk|
[ad. L. parasītic-us, a. Gr. παρασιτικ-ός, f. παράσιτ-ος: see parasite n. and -ic. Cf. F. parasitique (Littré).]
A. adj.
1. Of, pertaining to, or characteristic of parasites; having the nature of a parasite, sycophantic.
1627Hakewill Apol. (1630) 3rd Advt., The Bishop received small thankes for his parasiticke presentation. 1648Eikon Bas. xx. 197 Some parasitick Preachers. 1654Vilvain Epit. Ess. vi. 79 Parasitic Panegyrics. 1855Kingsley Westw. Ho! viii. (1869) 150 Somewhat of a gnathonic and parasitic soul.
2. Biol. Of, belonging to, or having the nature of a plant or animal parasite.
a. Living, as an organism, in or upon another from the body of which it derives its nourishment; pertaining to or of the nature of such an organism; also, by extension = symbiotic. In Path. applied to diseases caused by parasites.
Earlier naturalists included plants which grow upon others but are now known not to derive nourishment from them, e.g. polypody, moss, lichens.
1731–3Miller Gard. Dict. s.v. Hedera, Ivy..is a parasitick Plant. 1760J. Lee Introd. Bot. iii. iv. (1765) 169 Parasitic, when they grow not out of the Ground, but on some other Plant. 1799Hooper Med. Dict., Parasitic, animals..that receive their nourishment in the bodies of others, as worms, polypes, hydatids, &c. 1826Kirby & Sp. Entomol. xliv. IV. 213 The Ichneumons that are parasitic upon larvæ. 1851H. Spencer Social Statics iv. 449 In certain states of body, indigenous cells will take on new forms of life, and by continuing to reproduce their like, give origin to parasitic growths, such as cancer. 1861Miss Pratt Flower. Pl. IV. 80 Lesser Broom-rape..occurs chiefly on..clover, [but] is..parasitic on various other plants. 1899Allbutt's Syst. Med. VIII. 853 Parasitic diseases of the skin.
fig.1874H. R. Reynolds John Bapt. i. §6. 58 Some parasitic untruth which criticism was competent to cut away. 1878Geo. Eliot Coll. Breakf. P. 564 A parasitic growth on the vast real and ideal world of man and nature.
b. Applied to animals which do not provide for themselves, but depend in some way upon others for sustenance, e.g. by robbing them of their food, as the skua-gull, or by laying their eggs in others' nests, as the cuckoo.
1837Swainson Nat. Hist. Birds II. 196 The parasitic gulls (Lestris).. derive their chief supply of food by robbing their more feeble congeners. 1838Encycl. Brit. (ed. 7) XVI. 648 Lestris parasiticus, Ill. Parasitic Gull. 1860All Year Round No. 63. 296 Many bees are parasitic, and always lay their eggs in the nests of bees of other kinds. 1889Geddes & Thomson Evol. Sex xix. 278 The American cuckoo..is occasionally parasitic.
c. Used loosely or poetically of climbing plants, which depend on other plants or on something external for support. Now rare or Obs.
1830Hood Haunted H. i. ix, Vagrant plants of parasitic breed Had overgrown the Dial. a1845― Ode to R. Wilson xxiii, Faith is a kind of parasitic plant, That grasps the nearest stem with tendril-rings.
3. transf. (from 2.)
a. Applied to something subsidiary growing upon or attached to something else; spec. in Min. to minerals found upon or within other minerals; in Phys. Geog. to subordinate volcanic cones developed on the sides of the principal cone.
1811J. Pinkerton Petralogy I. 208 The most usual parasitic stones of granitel are schorl and garnets. 1878Huxley Physiogr. 194 Mount Etna..having its flanks studded with parasitic cones. 1891Freeman Sk. Fr. Trav. ii. ii. 112 A number of parasitic buildings on the south side [of a church].
b. Philol. Applied to a non-original vowel, consonant, or element, attached to an original phonetic element, out of which it has been developed, or to which it has been added; e.g. the d in thunder, the e in flower, the second element in the ‘parasite-diphthongs’ |eɪ, ɛə, əʊ, ɔə|.
1870March Compar. Gram. Anglo-S. Lang. 20 The consonants most difficult to make, the trills l, r, and the gutturals c, g, h, are often accompanied by an involuntary sympathetic movement of other parts of the organs, which produces what may be called a parasitic sound. 1871Pub. Sch. Lat. Gram. 8 Parasitic u or v follows q, ng, and s; as, sequor or seqvor; lingua or lingva; suavis or svavis.
c. Applied to trades: † (a) see quot. 1909; (b) non-productive.
1909Q. Rev. Jan. 83 The so-called parasitic trades—that is, trades in which it is alleged that workers who have incomes or maintenances derived from sources other than their wages underbid those who live entirely on their wages. 1926Spectator 19 June 1032/1 Far too much still goes in what we may call parasitic middlemen's profits.
4. Applied to unwanted subsidiary phenomena and effects in physical apparatus, esp. in electronic devices and electrical machinery.
1889Telegraphic Jrnl. 1 Nov. 497/1 If..the iron core were solid, the E.M.Fs. induced in it would..cause enormous currents to flow... They are currents which could not be utilised... By suitably dividing the iron core..these so-called parasitic currents may be rendered almost negligible. 1921Wireless World 15 Oct. 437/1 The..parasitic noise which abounds in amplifiers wired on the usual principle. 1927V. W. Pagé Mod. Aircraft (1928) vi. 206 (heading) Reduction of parasitic resistance. 1943F. E. Terman Radio Engineers' Handbk. vi. 498 Parasitic oscillations..are very likely to occur when large tubes are employed because of the long leads, large interelectrode capacities, and relatively high values of transconductance involved. 1958Nayler & Saunders Handbk. Aircraft Industry viii. 125 In modern aircraft the ‘parasitic’ drag due to extraneous items..has been largely eliminated. 1959Listener 25 June 1109/1 They are electric insulators and therefore do not carry parasitic electric currents (so-called eddy currents) when their magnetization changes rapidly. 1967Electronics 6 Mar. 251/1 With discrete components, parasitic capacitance from the diodes' packages increased the over-all capacitance. 1972Sci. Amer. Aug. 19/2 The Wankel operates with less friction than a conventional engine... The lower friction alone means decreased parasitic losses and can be translated directly into an increase in fuel economy.
5. parasitic bronchitis = hoose; parasitic gastritis, parasitic gastro-enteritis, in cattle, horses, or other domesticated animals, a gastric inflammation caused by parasitic nematode worms.
1925Vet. Rec. 19 Dec. 1137/1 Parasitic bronchitis is also known as husk, hoose, verminous bronchitis, or paper skin. It is a bronchial irritation, arising from the presence in the air passages of nematode parasites. 1942Skandinavisk Veterinär-Tidskrift XXXII. 488 (title) On parasitic gastritis in the horse. 1947New Biol. III. 49 The inflammation of the alimentary tract of sheep (and of that of other farm animals also) which is caused by parasitic roundworms is called by the veterinarian parasitic gastro-enteritis. 1951Vet. Rec. 22 Dec. 864/2 The literature presents certain references to the occurrence of parasitic bronchitis in adult cattle. 1965Ibid. 9 Oct. 1196/1 Field investigations into parasitic gastro-enteritis in the west of Scotland showed that Ostertagia ostertagi was the predominant parasite. Ibid., In Great Britain, outbreaks of bovine parasitic gastritis have been reported for many years. 1967W. R. Kelly Vet. Clin. Diagnosis vi. 27/2 (caption) Moderate degree of dyspnoea in a yearling heifer suffering from parasitic bronchitis.
6. Applied to an aerial that is not electrically connected to a transmitter or receiver.
1936L. S. Palmer Wireless Engin. xii. 469 Antenna B is not directly energised from the power source, but receives its current through the induction and radiation field of the directly energised antenna A. Antenna B..is sometimes called a parasitic antenna. 1947C. E. Tibbs Frequency Modulation Engin. vi. 114 When the parasitic aerial is at resonance.., and the separation between it and the energised aerial is held at 0·1λ, maximum radiation is in the direction of the parasitic aerial, which is then called a ‘director’. 1970J. Earl Tuners & Amplifiers v. 113 When a reflector and directors (called parasitic elements because they are not electrically connected to the dipole) are added to the system the centre impedance of the dipole falls well below 75Ω.
B. n. pl. Electronics. Parasitic oscillations.
1943F. E. Terman Radio Engineers' Handbk. vi. 498 Parasitics cause reduction in the power at the desired mode of operation, introduce spurious frequencies, give rise to distortion in linear amplifiers and modulators,..etc. 1967Electronics 6 Mar. 177/2 (Advt.), ‘Strays’, ‘streaks’, ‘parasitics’..you may forget them all. |