DAIRYING 35 



eggs and milk. Direct sunlight at noon is a stronger germ 

 destroyer than towards morning and evening, and diffused light 

 is less effectual in this direction than direct sunlight. It is also 

 true that germs protected by shadows or by a covering of dirt 

 may not be destroyed by even direct sunlight because it cannot 

 penetrate through the dirt. This shows why cleanliness and 

 scrubbing are beneficial to the public health. A sufficient num- 

 ber of windows in a cow stable not only makes the place a more 

 cheerful, but a more healthy habitation for both man and beast. 

 Vertical windows admit more light than horizontal windows of 

 the same size and the thickness of the wall in which the window 

 is placed has an influence on the amount of light passing through 

 the window. 



A good rule to follow in lighting a cow stable is to provide 

 four square feet of window space for each mature animal or 

 devote one-fourth the wall space to windows. 



718. Some Essential Points in Barn Ventilation. The nat- 

 ural forces that cause the passage of air through the flues and the 

 rooms connected with a properly constructed ventilating system 

 are first the pressure of the wind on the outside walls of the 

 building and second the difference in temperature and in 

 moisture content between the inside and the outside air. The 

 breath of the cows and the temperature of their bodies are 

 warmer than the air surrounding the stable and this makes such 

 inside air lighter than the colder air outside, so that it will rise 

 to the ceiling of the room in which the cows are standing. Dry 

 air is also lighter than moist air and this helps the circulation of 

 air in the stable. In order to take advantage of these conditions 

 of the air and the force of the outside wind as aids in procuring 

 desirable currents of air or ventilation through a cow stable, it 

 is necessary that the walls and windows of the stable, as well as 

 the air ducts and flues of the ventilating arrangements should be 

 made air tight, except where the intakes and the exits of air are 

 placed. 



719. Volume of Air Required per Cow. It has been esti- 

 mated* that the air drawn into and forced out of the lungs of a 



"Ventilation by F. H. King. 



