RESPIRATION. 



397 



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

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

 eter or a pneumo graph, 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. 193), 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 

 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. 

 194), 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 to 8. 



INSP. 



FIG. 194. A PNEUMATOGRAM. (After 

 Marey.) 



FIG. 195. A SPIROMETER. 

 (Baruttau.) 



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 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 

 is the spirometer, a modification of the gasometer. The form introduced by 

 Jonathan Hutchinson, of which Fig. 195 is a modification, consists of two 

 metallic cylinders, one containing water, the other containing air, the latter 

 being inserted into the former. The air cylinder is balanced by a weight so 

 accurately that it remains stationary in any position. A tube, penetrating 

 the base of the water cylinder, is continued upward through and above the 

 level of the water. The air-space above is thus placed in free communica- 

 tion with the external air. A stopcock at the outer end of this tube prevents 



