CHAP. IL] RESPIRATION. 363 



returns gradually to the normal, or may even rise to hyperpnoea 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 dyspnceic respiration alternating by gradual 

 transitions with periods of apncea. The cause of the phenomena 

 is not thoroughly understood. Stokes connected it with a fatty 

 condition of the heart, but it has been met with in various maladies. 

 Closely similar phenomena have been observed during sleep, under 

 perfectly normal conditions. It presents a striking analogy with 

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

 placed under abnormal circumstances. 



c \ 



