12 VENTILATION AND LIGHT. 



be so great as to starve the animal when he is turned 

 out, for though it is said to economise corn and lay on flesh 

 to have the animals kept warm, still it may be carried to an 

 improper excess. There is not generally sufficient discrimi- 

 nation exercised in the distinction between hot air and pure 

 air. Hot air is not always impure, nor is cold innocuous. 

 The fact is, other things being equal, a cubic yard of hot air 

 is certainly less nourishing than an equal quantity of cold air ; 

 because being more rarefied the former will of necessity 

 have less of the vivifying principle— the oxygen. Pure 

 atmospheric air ought to contain in one hundred measures, 

 seventy-three of nitrogen and twenty-seven of oxygen, nearly. 

 There is usually more or less carbonic acid gas mixed with 

 it, seldom, however, as much as one per cent. Now the 

 warmer the air in any confined place, the thinner it becomes 

 —it will be rarefied. Hence a stable filled with hot air, will 

 contain less oxygen than one maintained in cold, though 

 neither the one nor the other may be absolutely impure. 

 The operation of breathing destroys the oxygen and leaves 

 in its place a poisonous atmosphere, carbonic acid gas. 

 Now this is a heavy gas. It will remain at the bottom of 

 the stable unless forced upwards ; whereas the vapour and 

 hot air will always tend upwards whether there is an aperture 

 or not. So long therefore as the air in the stable and that 

 of the atmosphere are the same warmth, there will be little 

 ventilation. It is this interchange from hot to cold, which 

 causes the principle to be set in motion to its fullest extent ; 

 and the most perfect ventilation of air is when the cold and 

 pure air is admitted at the bottom of the building and the 

 hot air allowed to escape at the top. It is a mistake also to 

 imagine that the foul air from a stable can possibly escape 

 unless fresh and pure air is allowed free access." 



On such excellent and clearly defined principles comment 

 is needless. Having in a measure traced the cause, I will 

 pass to discuss the cfi'ect of inattention to these essential 

 rules. The effect, indeed, may be readily discovered in a 



