Glossary 645 



Vacuum system: A forced system of ventilation by which bad air 

 is drawn out of a building by fans, fresh air flowing in to take its 

 place. 



Ventricle (ven'tri-k'l) : One of the two lower chambers of the heart. 



Vermiform appendix (vur'mi-form a-pen'diks) : A short tube, closed 

 at the outer end, extending from the large intestine near its connec- 

 tion with the small intestine. 



Vertebrae (vur'te-bre) : The bones which make up the spinal column. 



Vertebrate: An animal with a backbone, or spinal column. 



Vibration: A regular moving to and fro, such as the movement of the 

 pendulum of a clock, or of a quivering musical string. 



Villi (viri) : Hair-like projections in the small intestine for the absorp- 

 tion of food. 



Virus (vi'rws) : The poison by which an infectious disease is spread. 



Vitality: Life force. 



Vitamins (vi'td-minz) : Substances in certain foods; essential for health. 



Volatile (vol'd-til) : Readily changed to vapor. 



Volcano: A hill or mountain, usually conical in shape, formed of cinders, 

 ashes, and molten rock thrown out by natural explosions or eruptions 

 from within the earth. 



Volt: The standard unit for measuring electromotive force or pressure. 



Voltage: Electrical pressure, measured in volts. 



Voltmeter: An instrument for measuring volts. 



Voluntary muscles: Muscles which perform movements under the guid- 

 ance of the will, such as movements of the arm and leg. 



W 



Water: A colorless, odorless, tasteless liquid, a compound of hydrogen 

 and oxygen ; essential to life. 



Waterspout: A tornado at sea in the form of a whirling column of 

 water. 



Water vapor: Water in the form of gas or in small particles floating 

 in the air. Steam from a tea kettle and the unseen moisture which 

 forms dew on cool objects are examples of water vapor. 



Watt: A unit for measuring the amount of work an electric current 

 can do. 



Weather: The condition of the atmosphere as regards temperature, 

 density, moisture and air motion. 



Weather Bureau : A division of the United States Department of Agri- 

 culture. It records weather statistics and predicts the weather. 



Weather graph: A graph showing the variation of a weather condition, 

 such as atmospheric pressure or rainfull, for a period of time. 



Wedge: A piece of wood or metal tapering to a thin edge. One of the 

 basic machines. 



Weight: The pull of gravity on a body; the resistance to be overcome 

 by a machine. 



Westerlies: Name given to the prevailing winds from the west. 



Wheel and axle: A variation of the lever, consisting of a solid cyl- 

 inder, or axle, to one end of which is attached a wheel or a handle. A 

 slight amount of force applied to the wheel or handle exerts great 

 turning force on the axle. The axle, in turning, winds a rope and 

 lifts a weight. One of the basic machines. 



White corpuscles (kor'pus-'lz) : Irregularly shaped, colorless cells 

 found in the blood. They destroy disease germs and aid in healing 

 wounds. 



