112 CAUSES AND PREVENTION OF DISEASE. 



But a sudden change in the outside currents may temporarily 

 reverse this series. 



With the windward window half open, the window on the 

 lee side being- open, the current passes directly through the stable 

 without mixing well with the air inside. 



If the window on the windward side is half open and the 

 lee window closed, then a strong entering current goes high to- 

 ward the ceiling, spreads out and diffuses in a very satisfac- 

 tory way through the stable air and finally escapes through the 

 ridge. If the windows are all closed, and a door open, then 

 the ridge gives a fairly regular outlet ventilation. The exact 

 movement of the air within the stable would be varied, of course, 

 by stall partitions and other obstructions. 



A strong wind passing over a stable provided with ventilat- 

 ing shaft may have an outward suction effect especially if some 

 provision is made to insure this result. This may be accom- 

 plished by putting a flange around the upper opening so as to 

 direct the outside current of air upward as it strikes the end 

 of the outlet shaft. 



Outlets. — In cases where suitable outlets are provided above, 

 and the conditions are favorable, warmed air passes upward and 

 out of the room or building, but if such outlets are not provided 

 then of course the heated air merely rises to the ceiling, cools, 

 spreads out and descends, and no pure air can come in to take 

 its place. If the outlets are too high the effects are practically 

 the same as though there were no outlets at all, for the air be- 

 comes cool before it escapes, and falls again. 



