298 THE SNAKES OF SOUTH AFRICA. 
and marvellous change takes place. It is no longer oxygen. 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 
Fic. 124.—The pipes which carry air to and from the lungs. 
They divide and sub-divide and penetrate to every part 
ofthelungs. They terminate in little bags orsacs. 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 belief has been 
exploded. ‘‘Colds’’ are caused by the attacks of microbes 
