58 SECOND-HAND AIR. 



thcit, though l)reathed again and again, until the breathing 

 animal dies. Consequently, iov all practical purposes, air with 

 16 per cent, of oxygen is very little better than none, and with 

 even twenty per cent, it would keep an animal depressed and. 

 starving for oxygen ; whereas air witli the full 21 per cent, feeds 

 him freely with the warming and invigorating gas. 



113. — When the oxygen has not only been destroyed, but its 

 place supplied with poisonous, depressing, carbonic acid gas, matters 

 are made still worse, as such air refuses to carry out the carbonic 

 acid gas that the blood cells bring back to the lungs and that 

 which is produced by combustion in the lungs themselves. 



ISTow a healthy full sized horse standing at rest in the stable, 

 will consume about 285,120 cubic inches of air every hour ; from 

 this he will extract 12,672 cubic inches of oxygen, and will 

 discharge into the air 10,768 cubic inches of carbonic acid gas. 

 This shows how necessary it is that the air of a stable should be 

 freely exchanged during the whole of the night, if the horse's 

 blood is to be kept in a state that will best tit him for his work. 



114. — The more we study this subject, and the more we 

 understand of the constitution ami internal economy of the horse, 

 the more shall we see of the importance of pure air, and how 

 inseparably it is connected with the warmth, vigour, health, and 

 efficiency of any warm ])looded animal. To try to warm an 

 animal by shutting the pure air away from it, is like trying to 

 increase the fire of a stove by shutting in the dampers, or to 

 make a candle burn brightly by putting an excinguisher on it. 

 The only reason that this is not always seen to be equally foolish 

 is that the beneficent laws of nature and the constitution of the 

 air itself do not allow us to exclude it effectually. 



Fortunately, air is not easily shut in or out of any place. Warm 

 air will escape upwards if it can, and cold air will rush into its 

 place. This law, added to the strong tendency of oxygen to 

 combine in the right proportion with nitrogen (111), prevents 

 thousands of persons from killing themselves and their horses 

 on the spot, as they would do if they could exclude air from their 

 buildings as easily and completely as they can shut out rain. 

 Perhaps we are wrong in calling anything fortunate that prevents 



