636 Our Surroundings 



Pleura (ploo'rd) : The membrane which covers the lungs. 



Plumbing: The pipes and fittings in a building for water supply and 



sewage disposal. 

 Plumule (ploo'mul) : The part of an embryo which develops above the 



cotyledon into the stem and leaf. 

 Point of saturation: The point at which air at a given temperature 



contains all the moisture it can possibly hold. 

 Polarity (po-lar'i-ti) : The tendency of a magnet to assume a north 



and south direction when suspended. 

 Pole: Either end of a magnet or of the earth's axis. 

 Pollen: A powder-like substance found in flowers and necessary to the 



development of their seeds. 



Pollination: The transfer of pollen in flowers. 

 Pollute (p<5-lut/) : To make unfit for use. 

 Porcelain: A semi-translucent kind of earthenware. 

 Porous: Full of small holes or spaces. 

 Portal circulation: The circulation of the blood through the liver; 



a part of the systemic circulation. 

 Portal vein: A large vein which carries blood from the capillaries in 



the walls of the small intestine to the liver. 



Potassium: A soft white metal which reacts violently with water. 

 Potential (po-ten'shal) : The amount of electrical pressure at a given 



point in an electrical circuit. 

 Potential energy: Possible energy; energy which exists but is not 



active ; same as latent energy. 



Power: Capacity to do work; rate of doing work. 



Precipitate (pre-sip'i-tat) : A solid which separates out when two solu- 

 tions are mixed. 



Precipitation (pre-sip-i-ta'shwn) : A fall of rain, hail, or snow. 

 Preserve: To keep from injury or from decay. 

 Pressure : The action of a force against an opposing force. 

 Primary colors: The seven colors of the spectrum red, orange, yellow, 



green, blue, indigo, and violet; in painting red, yellow and blue. 

 Principle of moments: In a lever the weight multiplied by the weight 



arm equals the effort multiplied by the effort arm. 

 Proboscis (pro-bos'is) : The feeding tube of insects. 

 Propeller: Two or more blades set at an angle on a shaft; used to 



propel a ship or an airplane. 

 Property : A quality of a substance. 

 Protein (pro'te-m) : A nutrient composed mainly of nitrogen; essential 



for the growth and repair of living tissues. 

 Proton (pro'ton) : A minute particle of positive electricity. 

 Protoplasm (pro'to-plaz'm) : A thin, nearly transparent fluid of which 



all living cells are made. 



Protozoa (pro-to-zo'd) : One-celled animals. 

 Pseudopods (su'do-podz) : Projections of protoplasm which form the 



false feet of some one-celled animals. 

 Ptomaine (to'ma-In) : A substance formed by the decomposition of 



organic matter; often poisonous. 

 Ptyalin (ti'd-lm) : A ferment in the saliva which helps digest starchy 



foods. 

 Pulley: A grooved wheel turning within a frame or block by means of 



a cord or rope passing over it. One of the basic machines. 

 Pulmonary circulation (pul'mo-na-ri) : The circulation of the blood 



through the lungs. 



