54 VETEEINAEY HYGIENE 



few 



any animal introduced into it would die in a 



seconds. 



In order that proper dilution of the air of buildings may- 

 be effected, about 150 times more air must be introduced 

 per hour than actually passes through the animal's lungs. 

 This appears difficult to understand, until it is explamed 

 that experimental inquiry has determined the limit of 

 impurity of the air of inhabited places, and to prevent this 

 amount of admissible impurity being exceeded, an eijormous 

 extra supply of fresh air is required. 



The limit of impurity of inhabited rooms was fixed by the 

 late Dr. de Chaumont as the result of numerous examina- 

 tions of the air of buildings. He found that the amount of 

 carbonic acid in the air of a room bore a relation to the 

 degree of impurity present. 



The actual amount of carbonic acid in itself was harm- 

 less, very much more could be breathed with impunity 

 than could be found in the worst ventilated room or stable, 

 but as a measure of the respiratory purity of the air, viz., as 

 an index to the probable amount of organic matter present, 

 it was found to give invaluable information. 



We cannot have the air of a stable as pure as the outside 

 air, it would require some millions of cubic feet per head 

 per hour to produce this, but we can have the air of the 

 stable sufficiently free from organic matter, to be unable to 

 detect on entering it from the outside air any difference in 

 the freshness of the two atmospheres. 



This is the basis of de Chaumont' s test ; it has been 

 applied over and over again in determining the sufficiency 

 of the ventilation of stables, and is found equally ap- 

 plicable to them as to barrack rooms, hospitals, and 

 prisons. 



If on entering an inhabited building from the outside air, 

 the sense of smell be at once recorded before it becomes 

 blunted, a very fair idea of the amount of impurity may be 

 obtained. If no sensible difference in smell can be deter- 

 mined, the air inside smelling as fresh as that outside, then 

 the amount of organic matter is at its lowest point, and 



Digitized by Microsoft® 



