RESPIRATION. 379 



The pause in Cheyne- Stokes respiration is somewhat less than 

 half of the duration of the active period. During the pause the 

 pupils are contracted and inactive; when respiration begins again 

 they become dilated and sensitive to light. The eyeball is usually 

 moved at the same time. Eyster has pointed out that with the Cheyne : 

 Stokes respiration there are also rhythmic changes in arterial tension. 

 (Traube-Hering waves.) He makes two groups of Cheyne-Stokes 

 respirations. In one group the dyspnoea coincides with a lowering of 

 arterial tension and a slow pulse-rate. In the other group the arterial 

 tension and pulse both increase in the dyspnoea and fall in the apncea. 

 He found that intracranial increase of blood-pressure produces Cheyne- 

 Stokes respiration. Douglas and Haldane have shown that Cheyne- 

 Stokes respiration is produced by the periodic occurrence and dis- 

 appearance of the (indirect) effects of want of oxygen on the respira- 



Fig. 137. Cheyne-Stokes Respiration. (WALLER.) 



tory center. The want of oxygen may be due to abnormal deficiency 

 in the alveolar oxygen pressure, or it may be due to effects on the 

 circulation of changes in the breathing, or to both causes combined. 



CHEMISTRY OF RESPIRATION. 



Looked at from a chemical point of view, respiration presents 

 the following phenomena : (1) absorption of oxygen; (2) exhalation 

 of carbon dioxide; (3) release of a certain quantity of nitrogen; (4) 

 exhalation of vapor of water. 



It has been previously stated that at each normal respiration of 

 atmospheric air but one-sixth of the air within the lungs is changed. 

 Haldane states that it is evident that at the end of each expiration the 

 air-passages up to the external openings of the nose and mouth are 

 filled with alveolar air. At the next inspiration this alveolar air has to 

 drawn back into the alveoli before fresh air begins to enter the latter ; 

 lence the part of each inspiration corresponding to this "dead space" 



