328 ARTIFICIAL INCUBATION 
within certain limits is permissible, but sudden fluctuations beyond 
this limit will preclude the maintenance of an even temperature 
within the machine. 
The room should be so constructed that it can be thoroughly 
and frequently ventilated, for fresh air is essential to the growing 
embryo, and good ventilation 
will carry off the fumes from 
the lamps. 
Arrangements should also 
be made to materially increase 
the moisture in theatmosphere 
when desired, since it has been 
proved conclusively that moist 
atmosphere is essential in incu- 
bation. 
Destgn.—These require- 
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4.4 
Fie, 155.—Working plans for incubator cellar. 
ments are best met by a house built partly below the ground 
(Fig. 155). The machines are then placed low, as this makes them 
less susceptible to changes of weather,—-the room will be cooler in 
summer and warmer in winter. Two courses are open: Either to 
put up an incubator room in some permanent building, or to con- 
struct a low one-story house specially for the purpose. The latter 
is the usual plan, and, all points considered, is undoubtedly the 
best. Where a room is fitted up in a building designed for other 
purposes, there is always danger of fire, and the rate of insurance 
is higher. Besides, unless the structure is exceedingly well built, 
the eggs are liable to be injured by shock or jarring from above. 
