DAIRY INSPECTION 135 
If the wind is very strong, air may also be forced out through 
the inlets on the leeward side, but ordinarily the right-angled 
bend in the inlets and the position of the outer opening at a 
lower level than the inner prevents or retards the escape of 
air through these inlets. In addition, wind passing over the 
top of an outlet shaft produces a suction action within the flue, 
and this draws air out of the stable. The force of this suction 
action increases with the height of the outlet shaft, because 
air movement or wind increases in velocity with the distance 
about the ground. 
The heat given off by the animals in the stable through 
the skin and in the respired air warms the stable air around them, 
expanding it and decreasing its density or weight, which causes 
it to rise toward the ceiling. Fresh air entering through the 
inlets, being colder and heavier than the air in the stable, gravi- 
tates toward the floor. Through the operation of these two 
currents the stable air and fresh air are mixed, the fresh air 
is warmed while the stable air is cooled and the moisture it 
contains is diluted. However, when the respired air is cooled 
below 81° F., it becomes heavier than fresh air of the same 
temperature because of the carbon dioxide which it contains and 
consequently settles toward the floor. For this reason, it is 
desirable to have the outlet flues arranged to draw air from 
the lower as well as the upper part of the stable. The expansion 
of the air in the stable by the animal heat increases the pressure 
within the stable and this has the effect of forcing air through 
the outlets; the construction of the inlets prevents air from 
being forced out through them. To obtain satisfactory results, 
the air in the stable should be about 20° F. warmer than the air 
outside. The effect of temperature differences on the draft in 
outlet flues increases with the length of the flue. The resistance 
encountered by air in passing through inlets and outlets modifies 
to some extent the effects of wind and heat. It is therefore 
desirable to have the outlet flues as straight as possible. 
Cloth Method of Ventilation—Stables may be ventilated by 
covering windows with muslin or cheese cloth. Glass windows 
should be alternated with the cloth-covered windows in order to 
permit sufficient light to enter the stable. Three square feet 
