VENTILATION OF STABLES. 47 



probably by the addition of oxygen, and certainty by the 

 agency of oxygen. If the air be destitute of this constituent, 

 or if it do not contain a certain- quantity, the blood can not 

 undergo the change by which it maintains life. 



The Composition of Impure Air is not always the same. 

 By impurity is here meant any alteration which renders the 

 air less fit for breathing. The impurity varies according to 

 the quantity, the number, and the kind of foreign matters 

 which mingle with the air, and according to the degree in 

 which one of its constituents is deficient in quantity. Air 

 may be bad, merely because it is deprived of part of its 

 oxygen. It is probable, indeed it is certain, that in particulai 

 situations the air does not contain its full proportion of 

 oxygen, and that the animals who breathe it do not experi- 

 ence any serious inconvenience. Though there is not the 

 usual quantity, there is sufficient. When the air contains so 

 little oxygen that it can not meet the demand of those animals 

 by whom it is breathed, it may very well be called bad. It 

 has power to do mischief; the animal suffers, not from the 

 presence of a pernicious agent, but from the absence of that 

 which enables the blood to perform its functions. The air, 

 however, may be rendered actively injurious or poisonous, by 

 the addition of foreign ingredients. These are of various 

 kinds, many of which can not be discovered by the chy'mist. 

 They are known to exist only from their effects upon the 

 health of the living animal. 



The Impure Air of a Close Stable is deficient in oxygen, 

 and mingled with carbonic acid, ammoniacal gas, and some 

 other matters. The deficiency of oxygen in stables has 

 never been proved by actual experiment. But there can be 

 no doubt but it occurs wherever the air is confined around a 

 breathing animal. Repeated investigations have shown a de- 

 ficiency in theatres, hospitals, churches, and other places 

 crowded by human beings. A French chymist analyzed the 

 air of a large theatre, that of the Tuileries, before and after 

 the play. He found it of the usual composition, 100 parts 

 containing 27 of oxygen and 73 of nitrogen, before the per- 

 formance ; at the conclusion, there were 76-^ of nitrogen, 2\ 

 of carbonic acid, and only 21 of oxygen. There is every 

 reason to believe that the air of a close stable is deficient in 

 oxygen to a much greater extent. Stables are often as 

 closely packed as a theatre ; the animals are much larger, 

 the building much lower, containing less air in proportion to 

 the demand closer, and closed for a longer time, than the 



