202 THE HORSE. 
HaAviNG THUS PROVIDED for the admission of fresh atmospheric air, the 
next thing to do is to carry it off, when it has been used for the purposes 
of respiration. As I before remarked, it is not safe to depend upon the 
wind for this purpose ; and the only remaining agent is the diminution in 
its specific gravity when air is warmed by respiration. By taking advantage 
of this principle, the foul air is carried off from the upper parts of the stable 
if a shaft is fixed there for its passage. Sometimes a small shaft is intro- 
duced over the head of each horse ; but in practice it is found that one 
larce shaft, about a foot square, will purify a stable containing four or five 
horses. It is better to fix this about the middle of the stable, as regards 
h sv SA es ee 
wi 
VENTILATING SHAFT. 
its length, but near the heads of the horses, as shown in the above section 
of a stalled stable. The tube may be made of wood—and, indeed, this 
material is better than iron, because it does not condense the steam as it 
ascends nearly so much as metal, and there is less dropping of water from 
it. The upper end of this shaft should be guarded from down-draughts, 
either by a cowl which will turn with the wind, or by a covered ventilator 
of galvanized iron fixed on the ridge of the roof, the price of which will 
HEAD OF SHAFT. 
depend on the size. At the bottom, a sheet of iron, considerably larger 
than the shaft, should be fixed about three inches below the mouth, so a3 
to prevent any down-draught striking the horses, and also to catch any 
drip from the condensation of the steam of the stable, as it comes in 
contact with the interior of the shaft. This, however, will be almost 
