298 



HUMAN PHYSIOLOGY 



lungs. This is followed by a slower outrush of air corre- 

 sponding to the active filling of the ventricles during the 

 beginning of ventricular diastole. Lastly, during the period 



of passive diastole, the cardio- 

 pneumatic movements of air are 

 in abeyance. 



These cardio-pneumatic move- 

 ments are of great importance in 

 animals which hibernate. Dur- 

 ing their winter sleep the ordi- 

 nary respirations almost stop, 

 but a sufficient gaseous inter- 

 change is kept up by these 

 cardio-pneumatic movements. 



FIG. 138,-To show relations of In the examination of the 

 Cardio-pneumatic Movements, heart sounds they must always 



A to Cardiac Cycle, B. In A be bome ^ mind> because; if 



there is any constriction in a 

 small bronchus near the heart, 

 the rush of air through this may give rise to a murmuring 

 sound, in character very like a cardiac murmur and syn- 

 chronous with the heart's action. On making the patient 

 cough, such a murmur at once disappears. 



the upstrokes are Expiratory, 

 the downstrokes Inspiratory. 



B. Interchange between the Air breathed and the Blood 

 in the Lung Capillaries. 



I. Effect of Respiration upon the Air breathed. To 



determine this, some method of analysing the air exhaled 

 must be employed. In the case of larger animals a mask 

 with a valve to allow the collection of the expired air may be 

 used, while small animals may be placed in a closed space to 

 which measured quantities of air are admitted, and samples 

 of the air drawn off, or the whole air drawn off, may be 

 collected and analysed. 



The following table shows the average percentage coin- 

 pos^tion of the air inspired and the air expired : 



Per Cent, of N. O. CO 2 . 



Inspired air . . .79 21 



Expired air . . . 79 17 4 



