June i, i92t 
Some Fundamentals of Stable Ventilation 
347 
This equation gives the theoretical value of the air flow per square 
foot of cross section. The actual flow of air is, however, less than the 
theoretical, its relative value depending on the resistance which the 
moving air has to overcome. It appears from an examination of the 
equation that in order to determine the flow of air the height and the cross 
section of the ventilator and the difference in temperature between the 
inside and outside air must be known. On the other hand, from the unit 
of air movement chosen and the difference in temperature likely to 
exist the minimum size of the ventilator can be determined. 
What difference in temperature can be maintained by the heat given 
off by the different animals when the ventilation is sufficient to supply 
the minimum amount of air needed is a question which will be considered 
later in its relation to heat emission. 
WATER VAPOR AS A MOTIVE POWER IN VENTILATION 
The water vapor which the animals give off is under ordinary condi¬ 
tions taken up by the moving air and carried off as rapidly as it is formed. 
The addition of the water vapor to the air in the stable tends to make it 
lighter than that outside, and this effect serves as a measure of the 
influence of water vapor as a motive power in ventilation. 
The higher the temperature of the air the greater is its moisture¬ 
holding capacity. The more moisture the air contains the lighter it is. 
Consequently, the motive power derived from the water vapor is greater 
the higher the temperature of the stable air and the more completely it 
is saturated. 
The quantities of water vapor produced by the different animals are 
given later. The motive power derived from the moisture is much less 
than that derived from the heat; and, since its magnitude largely de¬ 
pends on the difference in temperature, it can be considered only as 
secondary in importance. 
PRINCIPLES INVOLVED IN THE PRODUCTION OF HEAT BY ANIMALS 
The function of the animal heat as a motive power for stable ventila¬ 
tion has already been considered. A second function of the animal heat 
is to keep the stable warm in cold weather. The optimum tempera¬ 
ture to be maintained in the stable varies with the kind of animal and 
also with the ration. There exists also a certain relation between the 
heat given off by the animal and its thermal surroundings. For the 
purpose of estimating approximately the best stable temperature, both 
as regards comfort and economy, it appears desirable to turn to a 
consideration of the scientific principles involved. 
REGULATION OF BODY TEMPERATURE 
Farm animals belong to that general class known as warm-blooded 
animals, whose bodies during health maintain a nearly constant tempera¬ 
ture which is the resultant of two factors, thermogenesis, or the 
