CHAPTER XI 

 A STUDY OF RESPIRATION 



1. NECESSITY FOR RESPIRATION 



Definitions. Res-pi-ra'tion (Latin re = again and again 

 + spirare = to breathe) involves two distinct processes : 

 first, that of taking into the body new supplies of fresh air, 

 and secondly, that of removing from the body the impure 

 air that has been used. To the first process is given the 

 name in-spi-ra'tion (Latin in = into + spirare = to breathe); 

 the second is called ex-pi-ra'tion (Latin ex = out -f spirare 

 = to breathe). 



Necessity for Inspiration. Every contraction of the mus- 

 cles, every activity of the brain or of gland cells, involves 

 metabolism in these various tissues. We have seen that the 

 heart- beats more rapidly during exercise, and this means 

 that the red blood corpuscles are being hurried into mus- 

 cular tissue with their little boat-loads of oxygen. It is a 

 familiar fact, too, of everyday experience, that during the 

 activity of the various organs, we breathe more rapidly, for 

 as oxygen is in greater demand, more must be furnished to 

 the blood, or metabolism in the tissues will be retarded. 



Necessity for Expiration. Oxidation necessarily produces 

 a supply of the compounds we have classed as wastes. Even 

 when we are sleeping, the heart, the kidneys, many of the 

 various gland cells, and some of the nerve cells are at work, 

 and are therefore giving to the blood carbon dioxid, water, 

 and urea. If we take violent exercise, the amount of these 

 wastes is greatly increased, and if they are not thrown off 

 from the body, death will ensue, for they will finally stop 

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