RESPIRATION 197 



the jar ; the presence of carbon dioxide will be very evident. Repeat 

 the latter operation after allowing splinters to burn out in a jar of 

 oxygen. From these experiments it becomes evident that oxygen is 

 necessary in ordinary combustion, and that carbon dioxide is a 

 product of combustion. 



89. To show that Respiration increases the Amount of Carbon Diox- 

 ide in the Air. By means of a glass tube blow through lime water; 

 the white precipitate of carbonate of lime shows the presence of car- 

 bon dioxide in the breath. To show that most of this is a product of 

 respiration, pass some of the ordinary air of the room through lime 

 water ; the white precipitate is much smaller in amount. 



90. To illustrate a Difference between "Arterial" and "Venous" 

 Blood. Obtain some fresh ox blood at a slaughterhouse and "whip" 

 it to remove the fibrin and prevent clotting. By means of a carbon 

 dioxide generator, pass carbon dioxide gas through the blood; the 

 blood becomes darker. Now pass air through it, thus supplying 

 oxygen ; it becomes more scarlet in color. 



