152 



PRACTICAL PHYSIOLOGY 



this alternation of breathing and apnoea may continue for several 

 minutes or, it may be, hours. Some healthy men exhibit Cheyne- 

 Stokes respiration readily when they perform this experiment ; 

 others do not. 



FIG. 142. Cheyne-Stokes respiration. (Pembrey and Allen.) 



* Apnoea can be abolished by either (i) air containing 3 or 4 per 

 cent, of carbon dioxide, or (ii) pure oxygen, or (iii) air containing 

 a deficiency of oxygen, about 12 per cent, of oxygen. 



FIG. 143. Frog's heart. 



I, Normal ; 2, three minutes after one drop of 10 per cent, solution of muscarine ; 3, after the 

 application of a weak solution of atropine sulphate. The time is marked in seconds. 

 (Pembrey and Phillips.) 



