RESPIRATION. 179 



In its passage through the lungs it loses oxygen and gains CO 2 , 

 expired air consisting of 



Nitrogen, 79.557 



Oxygen, 16.033 



C0 2 4-38 



99.970 



The taking up of oxygen and giving off of CO 2 takes place by 

 the law of diffusion of gases, illustrated by simple experiments. 

 That expired air contains CO 2 may be shown by blowing into a 

 jar of lime-water, the liquid becoming turbid from the change into 

 carbonate of lime, and giving off of CO 2 in form of bubbles. These 

 bubbles, when collected, will not support combustion, and turn 

 blue litmus red. 



The greater part of the oxygen consumed is returned in the 

 form of CO 2 , about eight out of ten parts, the remainder being 

 thrown off by the urine and skin, or uniting with hydrogen in the 

 body. Solids and moisture in varying proportions are also thrown 

 off. 

 Changes in the Blood during Respiration. 



Arterial blood contains in one hundred parts 



Oxygen 20 volumes. 



Carbonic dioxide 36 



Nitrogen ,. 1-2 



Venous blood contains in one hundred parts 



Oxygen 8-12 volumes. 



Carbonic dioxide 46 



Nitrogen 1-2 



The oxygen exists in the blood in the red blood corpuscles as 

 oxy-hamoghbin, being given off in the peripheral capillaries, and 

 then is known as reduced hcemoglobin. 



The carbon dioxide exists in serum in a loose state or as soluble 

 carbonates. 



The nitrogen exists in solution in the blood serum, and can be 

 expressed by a small vacuum. 



The gases compose about 60 per cent, of the volume of the 

 blood. 



Nervous Mechanism of Respiration. 



Respiration is involuntary usually, as it is carried on during 



