208 APPLIED PHYSIOLOGY 



and it is significant that the mode of starting of the 

 first breath after birth, which was so long a fruitful 

 source of discussion, is now pretty generally attributed 

 to the effect upon the respiratory centre of the accumu- 

 lation of carbonic acid in the blood rather than to the 

 action on the centre of stimuli from the surface of the 

 body. That the latter can be powerful aids in stimu- 

 lating the centre to action, however, the good effect of 

 * spanking ' a newly-born infant which is disinclined to 

 breathe effectually proves. 



We have spoken hitherto as if there was only one 

 respiratory centre, and that wholly given over to the 

 superintendence of inspiration. It is probable, however, 

 that there is an expiratory centre as well, and that it 

 comes into play in the performance of forced expiration. 

 It may be excited reflexly, as in the act of coughing, or 

 by voluntary effort when it is desired to increase the 

 intrathoracic pressure, as in straining; and it would 

 seem also to react to peripheral sensory stimuli, and to 

 excessive venosity of the blood. Unlike the inspiratory 

 centre, however, it is not rhythmically active, for it 

 must always be remembered that the act of respiration 

 consists in a series of inspirations only, the expiratory 

 part of the process being, in normal conditions, purely 

 physical. 



The inverted type of breathing observed in young 

 children suffering from pneumonia is perhaps due to 

 stimulation of the expiratory centre. 



