134 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



or closed. The outlet flues must be air-tight and protected 

 against cold in exposed places. The best material for the 

 construction of these flues is galvanized iron (No. 28), 2 x 4 

 inch lumber being used in the corners and joints. Where the 

 shaft is exposed, the iron should be covered with %-inch boards. 

 Outlets may also be constructed of a double layer of tongued 

 and grooved boards with a layer of heavy building paper be- 

 tween. If tin or galvanized iron pipes are used, they should 

 be surrounded by a square wood frame and the interstices filled 



FIG. 10. An outlet flue hinged at the ceiling so that it can be drawn up out of the way. 



in with sawdust. Protection against cold is necessary because 

 the air in the outlet flue must be kept warm, otherwise it will 

 cease to ascend. The ceiling and walls of the stable should be 

 air-tight and should be constructed with a view to preventing 

 the radiation of heat as much as possible. 



The circulation of air through the stable results from the 

 operation of two factors, called by Professor King aeromotive 

 forces, namely: heat generated by the cattle, and wind. The 

 wind drives air through the inlets on the windward side of the 

 stable and thus increases the air pressure within the stable, as a 

 result of which air is forced out of the stable through the outlets. 



