344 
Journal, of Agricultural Research 
Vol. XXI, No. s 
The motive power utilized in stable ventilation is chiefly the passing 
wind and the heat and water vapor given off by the animals. It fre¬ 
quently happens, however, that the motive force due to the wind is very 
small or even zero. At such times the air movement is entirely depend¬ 
ent upon the motive power derived from a rise in temperature and from 
an increase in the moisture content of the air after it enters the stable. 
It is therefore important to know this minimum motive power—that is, 
the heat and water vapor supplied by the animals, as this knowledge is 
evidently fundamental in determining the proper dimensions of the ven¬ 
tilating system. 
But the heat given off by farm animals, while serving as a motive 
power for ventilation, is also relied upon to maintain the temperature 
of the stable at a comfortable degree in cold weather. The Committee 
on Farm Building Ventilation of the American Society of Agricultural 
Engineers in its recent report ( 8 ) to the society has emphasized very 
strongly the need of effective control of the temperature in farm build¬ 
ings, as based on a number of its investigations. The committee found 
many barns with well-equipped ventilating systems which were not pro¬ 
ducing satisfactory results to the owners, not because of inadequate ven¬ 
tilation, but because of the fact that the buildings were too cold. All 
these facts point to the necessity of knowing how much heat is given 
off by the different farm animals and is available for heating and ventilat¬ 
ing purposes. 
Besides heat and water vapor farm animals give off carbon dioxid 
and some volatile organic products. Air once respired contains carbon 
dioxid in a quantity which makes it unfit to be breathed again unless 
very much diluted with pure air. It is chiefly the carbon-dioxid content 
of the air that serves as a basis for determining its degree of purity. In 
selecting a unit of air movement in the construction of a ventilating sys¬ 
tem it appears, therefore, that a knowledge of the average amounts of 
carbon dioxid produced by the different animals must be of not a little 
significance. 
AMOUNT OF AIR REQUIRED FOR DIFFERENT SPECIES AND STANDARD OF 
PURITY 
From what has just been said it is clear that the question of stable 
ventilation is a question of maintaining the proper purity of air in the 
stable as well as the proper temperature. Air supports the life of the 
animal. The air an animal breathes is as much an indispensable part 
of the feed it consumes as is the hay or the grain eaten. Within the ani¬ 
mal body neither assimilation of food nor generation of energy can take 
place without the consumption of a proportionate amount of air. When 
the animals are outside they have plenty of pure air at their disposal; 
in the stable, however, the air is contaminated with the gases thrown 
off by them. Unless there is an air movement at a proper rate into and 
