646 Our Surroundings 



White matter: The white nerve tissue, consisting largely of nerve 

 fibers, forming the inside portion of the cerebrum and the cerebellum 

 and the outside covering of the medulla and the spinal cord. 



Wind: A horizontal, natural movement of the air. 



Wood alcohol: A poisonous alcohol made from wood fiber. 



Work: The overcoming of resistance. 



X-rays : Rays caused by an electric charge passed through a vacuum 

 tube, similar to light rays but of shorter wave length, capable of pass- 

 ing through flesh but not through bones, blood, or other substances 

 containing mineral matter. Used to locate foreign objects lodged in the 

 body, to discover growths on the internal organs, and to determine the 

 extent of injuries to bones either by means of direct vision or through 

 X-ray photographs of the parts affected. 



Yeast: A form of fungous plant which causes fermentation. Yeast is 

 used in bread making, as it combines with sugar, thereby forming gas 

 bubbles (fermentation) which lighten the dough. 



Zinc : A heavy, bluish-white metal. One of the elements. 

 Zones: Divisions of the earth according to temperature. There are two 

 frigid, or cold, zones, two temperate zones, and one torrid, or hot zone. 

 Zoology (z6-61'6-ji) : The science which treats of animals. 



