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TEXT-BOOK OF PHYSIOLOGY 



A graphic representation of the excursions of the thoracic walls, rhythmic 

 or otherwise, is obtained by fastening to the thorax an apparatus, a stethome- 

 ter or a pneumograph, which by means of a tambour takes up and trans- 

 mits the movement to a second tambour provided with a recording lever. 

 A simple form of pneumograph, suggested by Fitz (Fig. 192), consists of a 

 coil of wire two and a half centimeters in diameter and about 40 centimeters in 

 length, enclosed by thin rubber tubing, one end of which is closed, the other 



FIG. 192. PNEUMOGRAPH. 



placed in communication either with a tambour and lever or with a piston 

 recorder. By means of an inelastic cord or chain the apparatus is securely 

 fastened'to the chest. With each inspiration the spring is elongated, the air 

 within the system is rarefied, and as a result the lever falls; with each expira- 

 tion the reverse conditions obtain and the lever rises. If the lever be ap- 

 plied to the recording surface of a moving cylinder, a curve of the thoracic 

 movement, a pneumatogram, is obtained (Fig. 

 193), from which it is apparent that inspira- 

 tion takes place more abruptly and occupies 

 a shorter period of time than expiration; that 

 expiration immediately follows inspiration, 

 but that there is a slight pause between the 

 end of the expiration and the beginning of the 

 inspiration. The time relations of the^ two 

 movements can be obtained by a magnet-signal 

 actuated by an electric current interrupted 

 once a second. The ratio of inspiration to 

 expiration has been represented as 5 to 6, or 

 6 toS. 



<NSP. 



FIG. 193. 



A PNEUMATOGRAM. (After 

 Marey.) 



FIG. 194. A SPIROMETER. 

 (Boruttau.) 



Volumes of Air Breathed. The volumes of air which enter and leave 

 the lungs with each inspiration and expiration naturally vary with the ex- 

 tent of the movement, though four volumes at least, may be determined: 

 (i) that of an ordinary inspiration; (2) that of an ordinary expiration; (3) 

 that of a forced inspiration; (4) that of a forced expiration. 



The apparatus employed for the determination of these different volumes 



