78 VETERINARY HYGIENE 



amount of available oxygen is of no practical importance, men 

 and animals may suffer from oxygen starvation in badly ventilated 

 places owing to the heat and humidity which affect adversely the 

 absorption of this gas by the tissues. The amount of oxygen 

 in the air is also reduced by the combustion of gas and other 

 illuminants (except electric light) and by the fermentation and 

 oxidation of organic matter. Stale food, dirt and all substances 

 undergoing putrefaction withdraw oxygen from the air and liberate 

 ether gases in its stead. 



CARBON DIOXIDE INCREASE. Much importance was at one time 

 attached to the amount of this gas in inhabited places. It was con- 

 sidered to be distinctly deleterious to health if present in anything 

 but a very small percentage above the normal, but undoubtedly more 

 attention has been paid to it than was called for. 



The increase in the amount of carbon dioxide in the air resulting 

 from metabolism occurs part passu with other changes such as 

 decrease of oxygen and increase of organic matter, heat and 

 humidity, and as quantitatively it is estimated with comparative 

 ease it serves as a useful index of atmospheric pollution. Such, no 

 doubt, is its chief significance. 



If it is possible to ascertain what is the average amount of 

 carbonic acid gas excreted by each species of domestic animal dur- 

 ing any given period, when housed under normal conditions, then 

 one can form a fair estimate of the rate of general pollution. 

 Supposing that by experiment and careful observation under 

 practical conditions it is determined what is the maximum degree 

 of pollution that may be permitted in buildings, having regard to 

 the health of the animals contained therein, there should be no 

 difficulty in calculating the volume of fresh air that must be admitted 

 in order that the vitiation does not exceed such limit as may be set. 



The amount of carbon dioxide excreted during normal meta- 

 bolism by an average man while in a state of comparative quiescence 

 is 6 cubic foot per hour ; a large man undoubtedly produces 

 more than this, and there is also an increase with active work and 

 during the eating and digestion of food. The hygienist concerned 

 with the health of people has taken this as an average figure from 

 which to calculate the rate of vitiation and consequently the amount 

 of repurifying air that is required. 



Estimates given of the CO 2 excretion by the larger animals, 

 horses and cattle, differ considerably, which is to be expected as 

 the weight and surface area of the various types of horses and cattle 

 vary greatly. Furthermore, the amount of food consumed, and 

 to a certain extent its nature, have an important effect on the gaseous 



