CHAPTER YI. 



AIR. 



99. — 111 making provision for the sustenance of any animal 

 we are accustomed to think of food as the most important thing, 

 then of water, then of air. This is reversing the real order of 

 their importance, but it is natural, because food is the expensive 

 article, and the one left to our judgment and discretion. 

 We usually take the water as we find it, and we can do nothing 

 with the air except spoil it. But the trouble we have to procure 

 food and the unlimited provision which nature has made for the 

 free supply of air, should not mislead us as to their relative 

 importance. Whilst all three are indispensable for life, air 

 must stand first both in instant and imperative importance, 

 and in the necessity for its absolute purity. The food of the 

 ox may contain from 3 to 15 per cent, of nourishment, that of the 

 horse may range from 5 to 25, that of man from 10 to 50, that 

 of the bee from 50 to 90, but with all of them the air must contain 

 just about 21 per cent. Three per cent, excess would deprive 

 them of sense, and burn their lungs to ashes ; three per cent, 

 deficiency would slowly suffocate them, 



100. — By measurement the quantity of air demanded by 

 any warm blooded animal is beyond all comparison greater than 

 that of the food, but even by weight the lungs must be supplied 

 with aliout four pounds of oxygen for every pound of food 

 provided for the stomach. The water we drink is well filtered 

 before it can reach the blood, and the food is strictly confined to 

 the one long tube provided for it, and never comes in contact 

 with the blood, except such prepared portions of it as are 

 selected by the minute lacteals in the walls of that tube, No 

 such precautions are taken with the air ; nature has mixed it 



