622 Our Surroundings 



Dermis (dur'mis) : The sensitive skin below the epidermis, or outer skin 



of the body. 



Dew: Water vapor condensed on a cool surface. 

 Diagnosis (di-ag-no'sis) : Decision as to the nature of a disease from 



its signs and symptoms. 

 Diaphragm (di'd-fram) : The muscular floor of the chest; the adjustable 



opening of a camera; the metal sound disc in telephones and radios. 

 Diastase (di'd-stas) : A ferment in plants which changes starch to sugar. 

 Dicotyledon (di-kot-T-le'dwn) : A plant having two cotyledons, or seed 



leaves, such as the bean. 



Diet: A prescribed course of food intended as a health measure. 

 Diffused: Spread around or dispersed. 

 Digestion: The process of changing food in the body so it can be used 



to support life. 

 Digestive fluid: A fluid which helps change food so it can be used to 



nourish the body. 

 Digestive system: The organs in the body composing the alimentary 



canal, whose function is to change food into a form which can be used 



to support life. 



Dilate (di-lat') : To grow larger. 



Dilute (di-lut') : To weaken by mixing with water or some other fluid. 

 Diphtheria (dif-the'ri-d) : A dangerous infectious disease in which the 



throat and air passages are affected. 

 Dipping needle: A magnetized steel needle balanced to rotate vertically; 



used to locate magnetic ore and to locate the magnetic poles of the 



earth. 



Direct current: An electric current flowing in only one direction. 

 Dirigible balloon (dir'i-ji-b'l) : A long, pointed balloon which is pro- 

 pelled by engines and which can be steered. 

 Disease: A disordered condition of mind -or body; sickness. 

 Disinfectant (dis-in-fek'tant) : A substance used to destroy disease 



germs. 

 Dislocation: The displacement of a bone at a joint; usually the result 



of a blow or fall. 



Dispersal (dis-pur'sal) : The act of spreading or scattering. 

 Dissolve: To absorb a solid into a liquid. 

 Distillation (dis-ti-la'srmn) : The process of driving off gas or vapor 



from liquids or solids by heat and condensing this gas or vapor by 



cooling. The distilling of water to remove impurities and the making 



of coal gas from soft coal are illustrations. 

 Drug: Any substance taken as medicine; any narcotic. 

 Dry cell: A device to supply electric current; consists of a sealed zinc 



cylinder through the center of which runs a carbon rod, the space 



between being packed with certain chemicals. 

 Dry farming: The breaking up of the soil after each rainfall to retain 



moisture by retarding evaporation. Used in dry regions. 

 Dry ice: Solidified carbon dioxide gas, having a temperature of about 



109 below zero; often used in place of water ice. 

 Ductless glands (dukt'les) : Glands whose functions are to prepare and 



secrete hormones directly into the blood. These include the thyroid 



and adrenal glands and the spleen. 

 Dynamo: A machine for changing the energy of motion into electrical 



energy; consists of a soft iron core wound with insulated wire, the 



armature, which, by rotating within the magnetic field of one or more 



U-shaped electromagnets, produces an electric current. 



