352 



PHYSIOLOGY. 



Fig. 122. Marey's 

 Tympanum and Lever. 

 ( SANDERSON. ) 



A, Lever. B. Tympanum. 

 f. Tube which communi- 

 cates -with cavity of the 

 tympanum and connects 

 with the tracheal cannula 

 or the cardiograph. 



rubber membrane. The air is forced in between the two 

 layers until the external layer bulges outward. This 

 stethograph is placed in position on the chest by means of 

 tapes. The cavity of the saucer-shaped apparatus com- 

 municates with a recording tambour, which writes down 

 the movements on a revolving smoked drum. 



The -resultant curve, known as the pneumatogram, 

 shows that the acts of expansion and contraction of the 

 chest-wall consume nearly equal times. The ascending 

 limb (inspiration) is begun with moderate rapidity, be- 

 comes accelerated in the middle of its course, to be again 

 slowed at its end. The descending limb (expiration) shows 

 the same characteristics as to its construction, thereby 

 giving a gradual fall to the curve. 



INSPIRATION is SLIGHTLY SHORTER THAN EXPIRA- 

 TION. For all practical purposes it may be stated that the 

 average respiratory rhythm is : Inspiration : expiration : : 

 5 : 6. However, it is known that various authors give dif- 

 ferent ratios, and in women, children, and old people 6 to 

 8 or 6 to 9 may be found. Immediately following expira- 

 tion there is a slight pause. 



Cases are rather rare in which the dura- 

 tion of inspiration and expiration are equal, or 

 that of expiration shorter than inspiration. 

 When the respiratory movements are studied 

 as depicted on the pneumatogram, it is found 

 that there is practically no pause between the 

 end of inspiration and the beginning of expira- 

 tion. 



RESPIRATORY SOUNDS. 



If a stethoscope is placed over a portion of 

 a lung at some distance away from the trachea 

 and larger bronchi, a sound will be heard the 

 character of which is variously described as soft 

 or sighing, resembling the rustling of leaves in 

 a slight wind. The sound is heard during the 

 whole of inspiration and is followed by a short 

 expiratory sound. The inspiratory sound is 

 three times the length of the expiratory. It 

 must be remembered that the movements of 



