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Crutzen, Paul Jozef

(Encyclopedia)Crutzen, Paul Jozef, 1933–2021, Dutch atmospheric chemist, grad. Univ. of Stockholm (Ph.D. 1968, D.Sc. 1973). After working (1977–80) for the Nation...

Cumberland Gap

(Encyclopedia)Cumberland Gap, natural passage through the Cumberland Mts., near the point where Virginia, Kentucky, and Tennessee meet. The gap was formed by the erosive action of a stream that once flowed there. I...

Tydings, Millard Evelyn

(Encyclopedia)Tydings, Millard Evelyn tīˈdĭngz [key], 1890–1961, American politician, b. Havre de Grace, Md. He was admitted (1913) to the bar, soon built a successful law practice, and became (1916) a member ...

opiate drug

(Encyclopedia)opiate drug, any of a group of drugs derived from opium. Used medicinally to relieve pain and induce sleep, they include codeine, morphine, the morphine derivative heroin, and, formerly, laudanum. Som...

Hillman, Sidney

(Encyclopedia)Hillman, Sidney, 1887–1946, American labor leader, b. Lithuania. He emigrated to the United States in 1907. Beginning as a garment worker, he became a union leader after his key participation in a s...

antidiuretic hormone

(Encyclopedia)antidiuretic hormone ănˌtēdīyo͞orĕtˈĭk [key], polypeptide hormone secreted by the posterior pituitary gland. Its principal action is to regulate the amount of water excreted by the kidneys. An...

humus

(Encyclopedia)humus hyo͞oˈməs [key], organic matter that has decayed to a relatively stable, amorphous state. It is an important biological constituent of fertile soil. Humus is formed by the decomposing action ...

injection

(Encyclopedia)injection, introduction of a fluid into the body, usually by means of a needle and syringe. The material injected may be a test substance (as in determining allergic sensitivity or immunity to a disea...

Empedocles

(Encyclopedia)Empedocles ĕmpĕdˈəklēz [key], c.495–c.435 b.c., Greek philosopher, b. Acragas (present Agrigento), Sicily. Leader of the democratic faction in his native city, he was offered the crown, which h...

grinding

(Encyclopedia)grinding, process by which surface material is removed from an object, usually metal, by the abrasive action of a rotating wheel or a moving belt that contains abrasive grains. A grinding wheel can be...