SEC. 8. THE EFFECTS OF CHANGES IN THE 

 AIR BREATHED. 



The Effects of deficient Air. Asphyxia. 



When, on account of occlusion of the trachea, or by breathing 

 in a confined space, a due supply of air is not obtained, normal 

 respiration gives place, through an intermediate phase of dyspnoea, 

 to the condition known as asphyxia; this, unless remedial measures 

 be taken, rapidly proves fatal. 



Phenomena of Asphyxia. As soon as the oxygen in the 

 arterial blood sinks below the normal, the respiratory movements 

 become deeper and at the same time more frequent; both the 

 inspiratory and expiratory phases are exaggerated, the supple- 

 mentary muscles spoken of at p. 322 are brought into play, and the 

 rate of the rhythm is hurried. In this respect, dyspnoea, or hy- 

 perpncea as this first stage has been called, contrasts very strongly 

 with the peculiar respiratory condition caused by section of the 

 vagi, in which the respiratory movements, while much more pro- 

 found than the normal, are diminished in frequency. 



As the blood continues to become more and more venous the 

 respiratory movements continue to increase both in force and fre- 

 quency, a larger number of muscles being called into action and 

 that to an increasing extent. Very soon, however, it may be 

 observed that the expiratory movements are becoming more 

 marked than the inspiratory. Every muscle which can in any way 



