TECHNICAL INDEX AND GLOSSARY 



before that in the Orient. See "The Manufacture of Paper," 

 VoL VIII, p. 159. 



Parasitic Diseases. Diseases caused by animal or vegetable 

 parasites, such as the itch, caused by the burrowing under the 

 skin of the itch mite, or the disease trichinosis, due to the pres- 

 ence of trichinae burrowing in the tissues. See "Parasitic Dis- 

 eases," VoL IV, p. 204. 



Pepsin. A ferment secreted by the mucous lining of the 

 stomach, discovered by Schwann and Wasmann, 1836-1840. 

 When combined with an acid solution it has the power of trans- 

 forming coagulated albuminous substances into soluble pep- 

 tones. See "Animal Chemistry,"' Vol. IV, p. 128. 



Percussion. In medicine, the method of investigation which 

 consists in striking the surface of the body to ascertain from 

 the sounds produced the condition of the parts beneath. In- 

 troduced in modern times by Avenbrugger, and afterward 

 adopted by Laennec and Corvissart. See "Nineteenth Century 

 Medicine," Vol. IV, p. 199. 



Periodic Law. A term expressive of the observed fact that 

 the chemical elements when listed serially in the numerical order 

 of their atomic weights show a curious recurrence of similar 

 properties at intervals of eight elements. See "Periodicity of 

 Atomic Weights," Vol. IV, p. 64. 



Periscope. An optical instrument used for making observa- 

 sions from a submarine boat when submerged. See "Submarine 

 Vessels," Vol. VII, p. 93; in particular p. in. 



Phantoscope. A form of moving-picture machine. See 

 "Chrono-photography Moving Pictures," Vol. VIII, p. 248. 



Phlogiston. A hypothetical substance, at one time supposed 

 to be part of all bodies capable of being burned. The Phlogiston 

 theory was developed by George Ernst Stahl (1660-1734), fol- 

 lowing the experiments of Becker (1635-1682). See "The 

 Phlogiston Theory in Chemistry," Vol. IV, p. 3. 



Phonautograph. An instrument invented by Leo Scott in 

 1856, with which vibrations made by sounds were recorded on 

 smoked glass by means of a needle attached to a diaphragm. 

 See "The Edison Phonograph," Vol. VIII, p. 93. 



Phonograph. A device for recording and reproducing sounds, 

 invented by Thomas A. Edison in 1877. See "The Edison 

 Phonograph." Vol. VIII, p. 93. 



Photography. The art of producing pictures by the action of 

 light on chemically prepared surfaces. The first camera image 



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