| false projection | <ophthalmology> The faulty visual sensation arising secondarily to underaction of an ocular muscle. Synonym: erroneous projection. (05 Mar 2000) |
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| Fischer projection formula | <biochemistry> Of sugars, representations, by projection, of cyclic sugars, or derivatives thereof, in which the carbon chain is depicted vertically. The lowest-numbered asymmetric carbon atom (C-1 in aldoses; C-2 in 2-ketoses, e.g., fructose) is drawn at the top, and the rest of the carbon atoms of the chain are drawn in sequence below the top carbon atom. For each carbon atom, depicted in projection as lying in the plane of the paper, the carbon-to-carbon bond(s), which actually point away from the viewer, are drawn as vertical lines. The left-hand and right-hand bonds of each carbon atom, which actually point toward the viewer, are, in projection, depicted as horizontal lines. The conventions for the Fischer formulas of cyclic sugars are as follows: 1) if the highest-numbered asymmetric carbon atom has its OH (or its replacement) lying to the right, as is the 2-OH of d-glyceraldehyde, the sugar has the d configuration; if the OH is to the left, the sugar has the l configuration. 2) On the anomeric carbon atom (C-1 in the aldoses; C-2 in the 2-ketoses), an OH or substituted OH that lies to the right, with the OH of the highest-numbered asymmetric carbon atom also to the right is defined to be a; if it is to the left, with the OH of the highest-numbered carbon atom still to the right, it is b; the reverse applies if the latter OH is to the left. 3) The orientation of a terminal CH2OH group in the aldoses carries no configurational significance, as it contains no asymmetric carbon atom. (05 Mar 2000) |
| lateral projection | Radiographic projection with the X-ray beam in a coronal plane. (05 Mar 2000) |
| frog-leg lateral projection | A lateral projection of the femoral neck made with the thigh maximally abducted. (05 Mar 2000) |
| adolescent round back | Osteochondrosis of the vertebral epiphyses in children. (12 Dec 1998) |
| back | 1. Being at the back or in the rear; distant; remote; as, the back door; back settlements. 2. Being in arrear; overdue; as, back rent. 3. Moving or operating backward; as, back action. Back charges, charges brought forward after an account has been made up. Back filling, the retrograde movement of a man or body of men, without changing front. Back stream, a current running against the main current of a stream; an eddy. To take the back track, to retrace one's steps; to retreat. 1. In human beings, the hinder part of the body, extending from the neck to the end of the spine; in other animals, that part of the body which corresponds most nearly to such part of a human being; as, the back of a horse, fish, or lobster. 2. An extended upper part, as of a mountain or ridge. "[The mountains] their broad bare backs upheave Into the clouds." (Milton) 3. The outward or upper part of a thing, as opposed to the inner or lower part; as, the back of the hand, the back of the foot, the back of a hand rail. "Methought Love pitying me, when he saw this, Gave me your hands, the backs and palms to kiss." (Donne) 4. The part opposed to the front; the hinder or rear part of a thing; as, the back of a book; the back of an army; the back of a chimney. 5. The part opposite to, or most remote from, that which fronts the speaker or actor; or the part out of sight, or not generally seen; as, the back of an island, of a hill, or of a village. 6. The part of a cutting tool on the opposite side from its edge; as, the back of a knife, or of a saw. 7. A support or resource in reserve. "This project Should have a back or second, that might hold, if this should blast in proof." (Shak) 8. The keel and keelson of a ship. 9. <chemical> The upper part of a lode, or the roof of a horizontal underground passage. 10. A garment for the back; hence, clothing. "A bak to walken inne by daylight." (Chaucer) Behind one's back, when one is absent; without one's knowledge; as, to ridicule a person behind his back. Full back, Half back, Quarter back, players stationed behind those in the front line. To be or lie on one's back, to be helpless. To put, or get, one's back up, to assume an attitude of obstinate resistance (from the action of a cat when attacked). To see the back of, to get rid of. To turn the back, to go away; to flee. To turn the back on one, to forsake or neglect him. Origin: As baec, bac; akin to Icel, Sw, & LG. Bak, Dan. Bag; cf. OHG. Bahho ham, Skr. Bhaj to turn, OSlav. Bg flight. Cf. Bacon. Source: Websters Dictionary (01 Mar 1998) |
| back-action plugger | An instrument for condensing gold foil or amalgam in areas that cannot be reached directly. (05 Mar 2000) |
| back aperture | <microscopy> The exit pupil of a microscope objective lens. The objective lens back aperture, which can be examined with a phase telescope or by inserting a Bertrand lens, displays the conoscopic interference figure and diffraction patterns. (05 Aug 1998) |
| back cross | <genetics> A crossing of a heterozygous organism and one of its homozygous parents. (09 Oct 1997) |
| back focal length | <microscopy> As measured on the principal axis, from the second lens vertex to the back focal point of the lens. It is not the equivalent of the focal length. (05 Aug 1998) |
| back focal plane | <microscopy> The plane, normal to the lens axis, situated at the back focus of a lens. (05 Aug 1998) |
| back injuries | General or unspecified injuries to the posterior part of the trunk. It includes injuries to the muscles of the back. (12 Dec 1998) |
| back-knee | Hyperextension of the knee, the lower extremity having a forward curvature. Synonym: back-knee. (05 Mar 2000) |
| back lens | <physics> In any compound lens (a lens system composed of more than one lens element), the last lens through which the light passes is called the back lens. It may be a single simple lens, a doublet, or triplet. See: front lens (05 Aug 1998) |
| back mutation | <molecular biology> A mutation that causes a mutant gene to revert to its original wild-type base sequence. Compare: forward mutation. (09 Oct 1997) |