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A type of defective virus particle in which part of the genetic material of papovavirus SV40 is encased within an adenovirus protein coat (capsid). Human adenoviruses require human cells for their propagation; however, papovavirus SV40 can serve as…

A family of double-stranded DNA viruses, collectively known as adenoviruses, which are icosahedrally symmetric, usually found in the respiratory tract of the host species, and often associated with respiratory diseases. Members of the Adenoviridae…

A complex endocrine organ in proximity to the kidney. Adrenal gland tissue is present in all vertebrates from cyclostomes to placental mammals. The adrenal consists of two functionally distinct tissues: steroidogenic cells of mesodermal origin and…

A bacterial genus in the family Vibrionaceae comprising oxidase-positive, facultatively anaerobic, monotrichously flagellated gram-negative rods. The mesophilic species are A. hydrophila, A. caviae, and A. sobria; the psychrophilic one is A.…

A reaction in which suspended particles are aggregated or clumped. It occurs upon the admixture of another type of particle, a change in the composition of the suspending fluid, or the addition of a soluble agent that acts as a bridge between two or…

A substance that will cause a clumping of particles such as bacteria or erythrocytes. Of major importance are the specific or immune agglutinins, which are antibodies that will agglutinate bacteria containing the corresponding antigens on their…

An age-contingent reduction in physiological function and activity, with a concomitant increase in mortality rate and a diminution in reproductive rate. Aging is the process of becoming older, which is influenced by genetic and environmental…

A large, rabbit-sized rodent, belonging to the family Dasyproctidae and inhabiting South America and Central America, which is well adapted for speed because of its elongated hind legs. The agouti is a large rodent that resembles the rabbit or hare…

An order of actinopterygian fishes in the subdivision Elopomorpha, along with Elopiformes, Anguilliformes, and Saccopharyngiformes, all of which have a leptocephalous larval stage. Albuliformes, comprising three families, eight genera, and 30…

A plasma protein produced by the liver that maintains fluid balance in the blood and transports fatty acids in the plasma and interstitial fluid. It is the most abundant protein in human serum, and one of the first discovered and earliest studied…

An order of the class Anthozoa (phylum Cnidaria), containing 2500–3000 species, commonly referred to as soft corals, sea fans, sea whips, and precious coral. Members of the Alcyonacea are strictly marine. They occur from northern to southern polar…

A fluid-filled sac- or sausagelike, extraembryonic membrane lying between the outer chorion and the inner amnion and yolk sac of the embryos of reptiles, birds, and mammals. The allantois eventually fills up the space of the extraembryonic coelom in…

Any of a number of alternative forms of a gene. Allele is a contraction of allelomorph, a term that William Bateson used to designate one of the alternative forms of a unit showing mendelian segregation. New alleles arise from existing ones by…

Altered reactivity in humans and other animals to allergens (substances foreign to the body that trigger an allergic response) induced by exposure through injection, inhalation, ingestion, or skin contact. An allergy (or allergic reaction; Fig. 1)…

A large aquatic reptile of the family Alligatoridae. Alligators belong to the family Alligatoridae in the reptilian order Crocodylia (Crocodilia). Common usage generally restricts the name alligator to the two extant species of the genus Alligator.…

The study of changes in the characteristics of organisms with body size. Characteristics such as body parts or timing of reproductive events do not necessarily change in direct proportion to body size, and the ways in which they change relative to…

One of the four subclasses of Mammalia, containing a single order, the Multituberculata. The Allotheria first appeared in the Late Jurassic and survived well into the Cenozoic, a period of at least 100,000,000 years. Fossils are known from North…

Vicugna pacos, a member of the camel family (Camelidae), which has been domesticated for more than 2000 years and is economically important for its long, fine wool. The alpaca (Vicugna pacos; formerly, Lama pacos) [see illustration] belongs to the…

A glycoprotein that is normally present in significant amounts only in the serum of the fetus. It is produced in the yolk sac, the liver, and other tissues of the gastrointestinal tract. Its role is unknown, but alpha fetoprotein may function as a…

A fatty substance formed in the intestinal tract of the sperm whale (Physeter catodon). There is a question as to whether the origin of ambergris is normal or pathological, but it does serve as protection from the horny indigestible portions of the…

The tailless whip scorpions or whip spiders, an order of the class Arachnida. There are about 80 species in the tropics and subtropics. They are flattened, red to brown, and range from 5 to 45 mm (0.2 to 1.8 in.) in body length. All are nocturnal,…