In order that the blood may have an opportunity of absorbing the oxygen brought into the lungs, this membrane contains a network of tiny blood vessels or capillaries. The red corpuscles in the blood exchange the carbon dioxide waste, or as it is sometimes called, carbonic acid gas, for oxygen. It will, therefore, be seen that the air inhaled undergoes a radical change. When exhaled, its temperature is increased and it is laden with moisture given off by the lungs, and the carbonic acid gashas replaced the bulk of the oxygen which it contained.
We have briefly described what takes place during one respiration. Multiply this by the number of respirations per minute and the number of cows in the barn, and you will have some idea of the necessity of replacing with pure air the moisture-ladenair and poisonous gases given off.
Plenty of statistics could be shown to prove that the amount of oxygen taken out of the air once exhaled makes it absolutely unfit to be again inhaled until it has been mixed with a fresh supply of pure air.
Amount of Air Breathed Daily by Different Animals
Lbs. Cu. ft.
Horse 272 3,401
Cow 224 2,804
Pig 89 1,103
Sheep 58 726
Hen 2 29
Another Need for Ventilation
Aside from the bringing in of pure air to replace the oxygen being used up, a ventilation system is essential for removing the
moisture thrown off by the cattle.
It is estimated that approximately ten pounds of moisture, in the form of an invisiblevapor, is given off by each animal per day. With a herd of forty cows this would mean four hundred pounds of moisture every twenty-four hours that must be disposed of.
This vapor, if allowed to remain, will condense into moisture on the walls and ceiling of the barn.
One of the best evidences of a poor ventilation system is the frost which forms on the inside of the stable, caused principally by the fact that the moisture exhaled is not being carried off.
This moisture tends to decay the building and helps to contribute to the cold, damp, insanitary condition.
In addition to the moisture given off by the animal, it must be remembered that the incoming air is also moisture-laden.
To prevent condensation, it means that there must be an adequate and continuous movement of air. To give you some idea of the problem to be contended with, we show below another table which states the required number of feet of air per hour and per head, which must pass through the stable, to prevent condensation of moisture when it enters the stable 75% saturated and leaves it saturated at the stable temperature.
If the outside air
When the stable temperature is: 70
is 75% saturated at 30�
See Picture for chart
Page One Hundred Fifty-eight