RESPIRATION. 



355 



FIG. 172. PNEUMOGRAPH. (Fitz.) 



from moment to moment from sixteen to twenty. During sleep, 

 however, the respiratory movements often dimmish in nurrrber as 

 much as 30 per cent., at the same time diminishing in depth. 



Rhythm. Each respiratory act takes place normally in a regular 

 methodic manner, each event occurring in a definite sequence and 

 occupying the same 

 relative period of 

 time. This rhythm, 

 however, is not infre- 

 quently temporarily 

 disturbed ' by emo- 

 tions, volitional acts, 

 muscle activity, pho- 

 nation changes in the 

 composition of the 



blood, etc. ; with the removal of these disturbing factors, the respiratory 

 mechanism soon returns to its normal condition. 



A graphic representation of the excursions of the thoracic walls, 

 rhythmic or otherwise, is obtained by fastening to the thorax an 

 apparatus, a stethometer or a pneumograph, which by means of a tam- 

 bour takes up and transmits the movement to a second tambour 

 provided with a recording lever. A simple form of pneumograph, 

 suggested by Fitz '(Fig. 172), 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 with either 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 inspira- 

 tion the spring is elongated, the air within the system is rarefied, 



and as a result the lever falls; 

 with each expiration the reverse 

 conditions obtain and the lever 

 rises. If the lever be applied to 

 the recording surface of a moving 

 cylinder, a curve of the thoracic 

 movement, a pneumaiogram, is 

 obtained (Fig. 173), from which it 

 is apparent thaffinspiration takes 

 place more abruptly and occupies 

 a shorter period of time than expiratiorfl 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. 



173. A PNEUMATOGRAM.- 



Marey.} 



(After 



