THE CONTROL OF THE RESPIRATION 377 



tory movement, as in postapneic periodicity, or by some pathologic cir- 

 culatory disturbance. 



Periodic breathing is produced by forced respiration more readily in 

 rarefied air than at sea level. It was found by Douglas, 26 after breath- 

 ing forcibly for one minute at sea level, that the breathing when it 

 returned showed 8 to 10 different periods of apnea and hyperpnea. On 

 repetition of the experiment at an altitude giving a barometric pres- 

 sure of 600 mm., 25 such periods followed the apnea ; at a height cor- 

 responding to 520 mm., 40 periods. Indeed, at high altitudes periodic 

 breathing may be brought about by the slightest alteration in normal 

 respiration ; even taking a deep breath may be sufficient to cause distinct 

 periodicity in the succeeding respirations, and in many persons living 

 at high altitudes periodic breathing is very apt to occur during sleep. 

 As in pathological cases exhibiting Cheyne-Stokes respiration, the peri- 

 odic breathing at high altitudes can be immediately removed by inspir- 

 ing oxygen. 



We have devoted considerable space to a discussion of these extremely 

 difficult problems in the hope that clinical observers, by becoming ac- 

 quainted with the purely experimental work, may be in a position to 

 conduct more searching investigations as to the cause of Cheyne-Stokes 

 and other pathological forms of periodic breathing. 



