DEFINITION: 1 the sensation resulting from stimulation of the retina of the eye by light waves of certain lengths 2 the property of reflecting light of a particular wavelength: the distinct colours of the spectrum are red, orange, yellow, green, blue, indigo, and violet, each of these shading into the next; the primary colours of [...]

Colour Classification Systems People who make, sell, or use nail polish, lipstick, paint, ink, and many other products deal with very small variations in colour Colour classification systems have been developed that enable them to specify and obtain the precise colours they want. Some of these systems show how colours differ in ordinary daylight. Others [...]

Colour Vision in Animals Since animals cannot answer questions about the colours they perceive, scientists have had to develop experiments to find out whether animals can be trained to make choices on the basis of colour If an animal’s food is always placed under a red square instead of a green square and if the [...]

  DEFINITION: any of various hemipteran insects that live in fresh waters, including the back swimmers and the water boatmen. Even though they breathe air, several kinds of insects can also live underwater and are able to fly, crawl, or swim at will. Called water bugs, such insects belong to the order of true bugs [...]

DEFINITION:1 orig., venom, as of a snake 2 a) any of a kingdom (Virus) of prokaryotes, usually ultra microscopic, that consist of nucleic acid, either RNA or DNA, within a case of protein: they infect animals, plants, and bacteria and can reproduce only within living cells so that they are considered as being either living [...]

  DEFINITION: any of an order (Blattaria) of insects with long antennae and a flat, soft body: some species are common household pests. The cockroach is considered one of the most obnoxious of household pests. This brown or black insect can be found in houses, apartment and office buildings, ships, trains, and air planes in [...]

1981: AIDS diagnosed. A new fatal, infectious disease was diagnosed in 1981. Called Acquired Immunodeficiency Syndrome (AIDS), it began appearing in major cities among homosexual men and intravenous drug users. Other high-risk groups were haemophiliacs and other recipients of blood or blood products, babies born of AIDS-infected women, bisexual men, and prostitutes and their customers. [...]

Sexual precautions. Naturally, the most certain way to avoid an STD is to avoid sexual contact with infected persons. One sure way to do that is by sexual abstinence, meaning not having sex with anyone. Sexual abstinence in young adults is a normal and healthy choice. The next most certain way of avoiding an STD [...]

DEFINITION: 1 any of an order (Ephemeroptera) of delicate, soft-bodied insects with gauzy wings held vertically when at rest: in the adult stage, it lives only hours or a few days, but the aquatic larval stage may last for several years 2 an angler’s artificial fly made to resemble this insect. The delicate-winged mayflies with [...]

AIDS (acquired immunodeficiency syndrome), incurable disease caused by a virus that damages the human body’s immune system; believed to be transmitted through sexual contacts, blood transfusions, or contaminated needles used for intravenous drug injections; often fatal; high percentage of victims are homosexuals or drug abusers. The sports world was stunned on Nov. 7, 1991, when [...]