298 THE SNAKES OF SOUTH AFRICA. 



and marvellous change takes place. It has combined with the 

 poisons, and has changed them into a gas. This gas is called 

 carbonic-acid gas, or carbon-di-oxide. This we breathe out, and 

 thus get rid of many of the poisons in our blood. This air we 

 breathe out is poison in a gaseous form. If we could condense 

 it, we should see a mass of putrid filth. 



Now, think carefully over this wonderful mechanism which 

 God has provided for the casting out of poisons, and purifying 



Fig. 126. — The pipes which carry air to and from the lungs. 

 They divide and sub-divide and penetrate to every part 

 of the lungs. They terminate in little bags or sacs. There 

 are millions of them. (From Blackie's Physiology.) 



our blood, and remember if you want your blood to be pure, 

 you must breathe fresh air. You cannot get fresh air if you 

 live indoors, and shut out the pure air. You are breathing 

 poison when you do this. You are re-breathing your own breath, 

 or that of other people, and poisoning your blood, instead of 

 purifying it. Remember always to breathe pure, fresh air. 

 Flood your dwellings, offices, and workshops with it. Fresh 

 air and cool breezes don't give a " cold." That behef has been 

 exploded. " Colds " are caused by the attacks of microbes 



