Glossary 635 



Penumbra (pe-num'brd) : The lighter part of a shadow. 



Pepsin: A ferment in gastric juice which helps change protein food to 



a soluble form. 



Pericardium (per-T-kar'di-wm) : The membrane which encloses the heart. 

 Peristalsis (per-i-stal'sis) : The wave-like, muscular action which forces 



food through the alimentary canal. 

 Peritoneum (per-i-to-ne'zim) : The membrane lining the walls of the 



abdomen and the outside of the stomach. 

 Petiole (pet'T-6l) : The stem of a leaf. 

 Petri dish (pa'tre) : A dish used to hold a medium on which to grow 



bacteria. 

 Petroleum (pe-tro'le-wm) : Mineral oil; a dark-colored, inflammable 



liquid found by drilling into the earth. 

 Pharynx (far'inks) : The cavity at the back of the mouth, which leads 



to the esophagus. 

 Phases of the moon: The constantly changing forms in which the 



moon is seen, such as half moon, full moon, and crescent. 

 Phenomenon (fe-nom'e-non) : Any fact or event which can be observed 



by the senses. 



Phonograph: A machine for reproducing sounds recorded on a record. 

 Phosphate: A mineral substance needed by the body; a fertilizer con- 

 taining phosphorus. 

 Phosphorus : A solid, yellowish, wax-like^ inflammable substance that 



readily absorbs oxygen from the air. One of the elements. 

 Photoelectric cell (fo-to-e-lek'trik) : An electric device used to vary 



the strength of an electric current to correspond to variations in the 



intensity of a beam of light. 

 Photosphere (fo'to-sfer) : The part of the sun which we commonly see, 



consisting of brilliantly burning gas. 

 Photosynthesis (fo-to-sin'the-sis) : The making of carbohydrate food 



in the green leaves of a living plant exposed to the sun. 

 Physical change: A change in which the nature or composition of a 



substance remains the same, as logs made into lumber. 

 Physical culture: Systematic exercise of the muscular system. 

 Physical geography: The science which treats of the earth's surface 



and its history. 

 Physical property: Any property of a substance that can be observed 



by the senses of sight, hearing, taste, touch, or smell. 

 Physicist (fiz'i-slst) : A specialist in the science of physics. 

 Physics: The science which treats of mechanics, heat, electricity, light 



and sound. 

 Physiological division of labor (fiz-i-6-16j'T-kal) : Performance of 



various kinds of work by different parts of an organism. 

 Physiology (fiz-i-ol'o-ji) : The science which treats of our bodies. 

 Piano player: A piano played by air pressure. 

 Pinnate leaf (pin'at) : A netted-veined leaf of feather-like form. 

 Piston: A sliding solid cylinder within a larger hollow cylinder, moved 



either by expanding gas or steam, as in an engine, or by hand or 



other force, as in- a pump. 



Pith : A very light, woody, substance ; the central part of a stem. 

 Planet: A large, spherical body that revolves around the sun, such as 



the earth. 



Plant: Any vegetable growth. 

 Plasma (plaz'md) : The liquid part of the blood. 

 Platinum: A solid, very heavy, silvery metal. One of the elements. 



