klsi-iRATION 125 



Regulation of Respiration. The respiratory centre 

 can be influenced so that the impulses it sends out are 

 modified in strength, character, or frequency. Thus if there is 

 anything irritating the trachea or larynx impulses pass from 

 them along the sensory nerves (and the sensory nerves of the 

 trachea and larynx are branches of the vagus nerves) to the 

 spinal bulb, and these impulses so influence the respiratory 

 centre that it sends out powerful impulses to the expiratory 

 muscles, and a cough is the result. Again, a dash of cold 

 water will cause a sudden strong inspiration. This is caused 

 by impulses passing along the sensory nerves of the skin to 

 the central nervous system, and so to the respiratory centre, 

 < ausing it to send out strong impulses to the ihspiratory 

 muscles. When a man is running his respiration is quickened ; 

 this is due to the blood of the body containing the large 

 amount of waste products produced by the violent muscular 

 contraction ; more oxygen is used up and more carbonic acid 

 is formed. A deficiency of oxygen and an increase of carbonic 

 acid in the blood, together with the presence of other sub- 

 stances formed by muscular contraction, so act, when the blood 

 reaches the spinal bulb, on the respiratory centre as to 

 stimulate it to greater activity, and cause it to send out 

 impulses faster ; hence a quicker respiration is the result. 



Asphyxia. -If air cannot pass vnto and out of the lungs, 

 as, for example, when there is something blocking the larynx 

 or trachea, such as some food which has "gone the wrong 

 way," the blood gradually becomes more and more venous, that is, 

 more and more charged with carbonic acid and more and more 

 deficient in oxygen. The first effect of the obstruction is to 

 lead to coughing, violent expiratory efforts, the object of which 

 is to remove the obstruction. This coughing is caused, as 

 we have seen, by the action of sensory impulses brought from 

 the larynx to the respiratory centre. If this does not succeed 

 in removing the obstruction, the blood gradually becomes more 

 and more venous, more and more charged with carbonic acid, 

 and more and more deficient in oxygen. This venous blood 

 acts on the respiratory centre so as to stir it up to increased 

 activity, and it sends out nervous impulses, which cause not 

 only quicker respiration, but much more powerful inspirations, 

 followed by more powerful expirations. Such a condition of 



