CHAP. IL] RESPIRATION. 637 



375. Secondary Respiratory Rhythm. Cheyne-Stokes Re- 

 spiration. A remarkable abnormal rhythm of respiration, first 

 observed by Cheyne but afterwards more fully studied by Stokes, 

 and hence called by their combined names, occurs in certain 

 pathological cases. The respiratory movements gradually decrease 

 both in extent and rapidity until they cease altogether, and a 

 condition of apncea, lasting it may be for several seconds, ensues. 

 This is followed by a feeble respiration, succeeded in turn by a 

 somewhat stronger one, and thus the respiration returns gradually 

 to the normal, or may even rise to hyperpncea or slight dyspnoea, 

 after which it again declines in a similar manner. A secondary 

 rhythm of respiration is thus developed, periods of normal or 

 slightly dyspnoeic respiration alternating by gradual transitions 

 with periods of apncea. The cause of the phenomena is not 

 thoroughly understood. Whether the waning and waxing of the 

 respiratory inovements be due to corresponding rhythmic changes 

 in the nutrition of the respiratory centre itself, or to a rhythmic 

 increase and decrease of inhibitory impulses playing upon that 

 centre from other parts of the body, for instance from higher 

 regions of brain, has not yet been settled. It frequently appears 

 in connection with a fatty condition of the heart, but has been 

 met with in various maladies. Closely similar phenomena have 

 been observed during sleep, under perfectly normal conditions ; 

 and this fact is rather in favour of the latter of the two explana- 

 tions just given. The phenomena present a striking analogy with 

 the 'groups' of heart-beats so frequently seen in the frog's ventricle 

 placed under abnormal circumstances. 



