98 



VETERINARY HYGIENE 



force is reduced. Galvanised cast-iron gratings and hit-and-miss 

 gratings are sometimes used, but they are subject to the same 

 objections as air bricks. Hit-and-miss gratings invariably get 

 clogged with dust and corrosion and fail to work satisfactorily. 

 " Hit-and-Miss " Windows should not be confused with hit- 

 and-miss gratings. The windows re- 

 ferred to are invariably constructed of 

 wood and are either wholly for the pur- 

 pose of admitting air by control, or 

 partly for such and partly for lighting, 

 any lighting part being filled in with 

 glass. These windows probably derive 

 their designation from being fitted into 

 openings in the wall which were origin- 

 ally intended for ordinary windows. 

 The hit-and-miss part consists of a 

 board with slot perforations about three-quarters of an inch wide and 

 of any length, the solid spaces between each slot may be about one 

 inch or an inch and a half wide. Another board similarly slotted 

 is fixed in grooves on the inside or outside (usually the former) in 

 such manner that by the aid of a small knob screwed into the centre 



FIG. 35. A Drain Pipe form- 

 ing a direct air inlet. 



FIG. 36. A Bent Pipe Air Inlet in 

 which the air is directed up- 

 wards. An alternative method 

 is to bend the pipe downwards on 

 the outside of the building, as 

 shown by the broken lines, in 

 order to check the force of the 

 incoming air. 



FIG. 37. A Box Air Inlet fitted with 

 a grating on the outside and a 

 regulating valve on the inside. 

 The incoming air is directed 

 upwards. 



of the sliding part it may be moved to regulate or entirely close the 

 apertures. This type of ventilator cannot be recommended in con- 

 sequence of its liability to jamb either by reason of wet, which causes 

 the wood to swell, or in consequence of the invariable collection of 

 dirt, dust and grain between the boards. In any case they are 

 usually situated half-way up the wall of the stable or byre near the 

 mid-stratum of contained air without any provision for turning the 



