620 Our Surroundings 



Circulatory system (sur'ku-ld-to-ri) : The system through which the 

 blood circulates in the body. It consists of the heart, the arteries, the 

 veins, and the capillaries. 



Cirrus (si r '^ s ) : A thin, broken, fleece-like cloud. 



Civil day: A day of exactly 24 hours, running from midnight to mid- 

 Clay: A common earth, soft and plastic when wet, hard when baked. 

 Used in the making of pottery, bricks, and tiles. 



Climate: The average weather conditions over a long period. 



Clinical thermometer (klm'i-kal) : A Fahrenheit thermometer in which 

 the mercury remains at the highest temperature recorded until shaken 

 down. Used to record bodily temperature. 



Clotting: Coagulation, or thickening, of blood. 



Clouds: Masses of water vapor condensed high in the air. 



Coagulation (ko-ag'u-la-shwn) : Thickening, as the thickening of blood 

 from a wound. 



Coal: A hard, black, natural fuel composed largely of carbon. 



Cocaine (kd'kd-m) : A narcotic drug made from the dried leaves of the 

 coca plant. Used to deaden pain. 



Cochlea (kok'le-d) : A spiral tube full of liquid which transmits sound 

 waves from the middle ear to the auditory nerve. 



Codein (ko-de'in) : A narcotic drug made from opium. 



Coffee: A beverage containing a stimulating substance called cafTein ; 

 made from the roasted seeds of the coffee plant. 



Coke: Soft coal from which gaseous substances have been removed by 

 heating; used as a fuel. 



Combustion: Burning. 



Comets: Heavenly bodies with bright heads and long luminous tails, 

 which travel around the sun. 



Communicable disease: A disease which can be imparted from one per- 

 son to another. 



Commutator (kom'u-ta-ter) : A device used on a dynamo for changing 

 an alternating current to a direct current. 



Compass: An instrument used to determine direction. Its essential part 

 is a magnetized steel needle which tends to point north and south. 



Composition: The kinds and proportions of materials of which a thing 

 is made. 



Compound: A substance formed by the chemical union of two or more 

 elements. Water is a compound of oxygen and hydrogen. 



Concave: Hollowed or curved inward as the inner surface of a hollow 

 ball. 



Concrete: A mixture of cement, sand, and broken stone, moistened with 

 water. It becomes solid, rock-like, and durable when it sets and dries. 

 Widely used in the construction of roads, sidewalks, dams and build- 

 ings. 



Condensation (kon-den-sa'shwn) : The change from a gaseous to a 

 liquid form, as the condensation of water vapor in forming dew. 



Condenser: A device for accumulating and holding a large charge of 



electricity in a small space. 



Conduction (k<5n-duk'shMn) : The flow of heat through a body, or from 

 one body to another body through contact. The handle of a dish con- 

 taining hot liquid becomes heated by conduction, as does a hand which 

 grasps the handle. 



Conductor: A substance through which heat will pass readily. A sub- 

 stance through which an electric current will pass readily. 



