RESPIRATION 



Yawning* consists of a slow deep inspiration per- 

 formed with the mouth widely open, and succeeded by 

 a slow expiration accomplished with a gaping mouth 

 and contracted glottis, which produces the well-known 

 sound. It is apparently the result of a fatigue of atten- 

 tion, and therefore appears most readily when the brain 

 is easily exhausted, as in the subjects of anaemia. The 

 stretching of the limbs which accompanies it is believed 

 to be an attempt to overcome the stasis of blood in the 

 muscles, and to drive it to the brain. 



Laughing and crying are, like sobbing, results of 

 disordered action of the respiratory centre brought about 

 by emotional influences. 



The peculiar rhythmical form of breathing which goes 

 by the name of Cheyne-Stokes respiration is probably 

 due to periodic variation in the automatism of the 

 respiratory centre. This periodic variation shows itself 

 when the influence of higher regulating centres is 

 removed, as may happen, for example, in uraemic 

 poisoning, and perhaps also simply as a result of a 

 lowering of the activity of the respiratory centre itself. 

 When the sensitiveness of the respiratory centre is 

 lowered, it does not respond to the stimulus normally 

 given by an excess of carbonic acid in the blood until 

 this has reached an unusual degree. A series of deep 

 inspirations is then initiated, which result in very 

 perfect ventilation of the lungs, and the carbonic acid 

 is so thoroughly removed that a period of apnoea sets 

 in until enough of it has accumulated to stimulate the 

 centre once again. That this explanation is correct 

 seems to be proved by the fact that Pembrey has been 



