| positive focal length | <microscopy> Any lens which converges parallel rays to a focus at the back of the lens is a positive lens and has a positive focal length. The focal length is measured from the second principal point of the lens to the point on the lens axis where the rays from an infinitely distant point are brought to focus. See: negative focal length. (05 Aug 1998) |
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| positive G | Gravity or acceleration in the usual head-to-foot direction in flying or in standing upright; the reverse of negative G. (05 Mar 2000) |
| positive image | <microscopy> A developed image in which dark areas correspond to dark areas of the original subject. (05 Aug 1998) |
| positive lens | <physics> Any lens with a positive focal length. Such lenses are thicker in the centre than around the circumference. There are three types of positive lenses, double convex or biconvex, planoconvex, converging concavoconvex or converging meniscus. (05 Aug 1998) |
| positive meniscus | A convexoconcave lens in which the power of the convexity exceeds that of the concavity. Synonym: positive meniscus. (05 Mar 2000) |
| positive ocular | <microscopy> A Ramsden ocular or any modification of it. The diaphragm is below the field lens. (05 Aug 1998) |
| positive phase | The period following the negative phase, during which the opsonic index rises. (05 Mar 2000) |
| positive rays | Those originating in a gas discharge tube and moving in a direction opposite to that of cathode ray's; made up of positively charged ions. Synonym: positive rays. (05 Mar 2000) |
| positive scotoma | A scotoma that is perceived as a black spot within the field of vision. (05 Mar 2000) |
| positive stain | <technique> Direct binding of a dye with a tissue component to produce contrast; in electron microscopy, heavy metals like uranyl and lead salts are used to bind to selective cell constituents to produce increased density to the electron beam, i.e., contrast. (05 Mar 2000) |
| positive strand RNA viruses | Class IV and VI viruses that have a single stranded RNA genome that can act as mRNA plus strand) and in which the virus RNA is itself infectious. Includes Picornaviridae, Togaviridae and Retroviridae. (18 Nov 1997) |
| positive supporting reactions | Consisting of those reflex muscular contractions whereby the body is supported against gravity; seen in an exaggerated form in the decerebrate animal, negative supporting reaction's, consisting of inhibition of the extensor muscles and unfixing of the joints which thus enable the limb to be flexed and moved into a new position. Synonym: supporting reflexes. (05 Mar 2000) |
| positive taxis | The attraction of protoplasm toward a stimulus. (05 Mar 2000) |
| positive thermotaxis | Attraction of a plant or animal to heat. (05 Mar 2000) |
| positive transference | Transference characterised by predominantly friendly, respectful, and positive feelings on the part of the patient toward the analyst. (05 Mar 2000) |