96 



VETERINARY HYGIENE 



or cow must be doubled. This, of course, applies to all forms of 



wall ventilators (see the table on page 94). 



Horizontally centre - pivoted windows 

 (figure 33) are satisfactory in sheltered parts 

 of a building, but are not so useful as the 

 hopper type for exposed positions, because 

 with a wind of any force the incoming air 

 cannot be properly controlled, with the con- 

 sequence that such windows are more often 

 shut than open. 



Tobin Tubes. These are illustrated in 

 figure 34. The air enters the tube at a low 

 level outside the building and passes up a shaft, 

 usually about 5 feet high, and then spreads out 

 in the building without causing a draught. 

 Though commonly used in human dwellings, 

 public halls and the like, they are not generally 

 adopted in animal buildings in this country, 

 though they form an integral part of the King 

 system as practised in America. They may 

 be built in the wall or take the form of a box- 



FIG. 3 2.-Section of a Hopper shaft inside the building against the wall. The 



Window. The side guards 



are not shown. former method is better for animal buildings. 



Direct Inlet Pipes or Boxes. Very simple and effectual air in- 



FIG. 33. Centre-pivoted Window. Section and elevation. 



