X 



CHAPTER XI 

 RESPIRATION 



Arterial and Venous Blood. Get some blood at a 

 butcher's and defibrinate it. Put some of the blood into two 

 bottles. Pass carbonic acid gas into one bottle, shaking at the 

 same time. Shake the other with air, and after a few minutes 

 notice the colour of the blood in each. The blood shaken with 

 air is scarlet as before, or even brighter ; the blood shaken with 

 carbonic acid is dark reddish-purple. Take some of the dark 

 purple blood out and shake it up with air it becomes scarlet 

 again. The colour of the blood is entirely due to the haemo- 

 globin of the red corpuscles, and haemoglobin is reddish-purple 

 in colour. When blood is exposed to air the haemoglobin 

 takes up oxygen from the air and becomes oxyhaemoglobin, 

 and this is scarlet in colour. When blood is exposed to 

 carbonic acid gas, or to air containing but little oxygen, the 

 oxyhaemoglobin parts with oxygen and becomes haemoglobin 

 again. Thus haemoglobin has the power of taking up oxygen 

 into loose chemical combination, and of readily giving it up 

 again. 



The blood in the left chambers of the heart and in the 

 arteries of the general circulation is bright scarlet in colour. 

 Bright scarlet blood is therefore called arterial blood. The 

 blood in the veins of the general circulation and in the right 

 chambers of the heart is dark reddish -purple. Reddish- 

 purple blood is therefore called venous blood. When venous 

 blood is shed it comes in contact with the air, and the haemo- 

 globin in it which is not already united with oxygen takes up 

 oxygen from the air and becomes oxyhaemoglobin, so that the 

 blood soon becomes brighter in colour and nearly as bright as 



