292 
THE ART OF REARING 
exterior are nearly equal, all the window-frames 
may be opened, and the Italian shutters must be 
closed, at least the greatest part of them. 
T made eight ventilators in two lines in the 
floor, and in the ceiling, placed perpendicularly 
opposite each other, in the centre of the passages 
between the wicker hurdles. These ventilators 
had sliding pannels, made of thick glass, to close 
them and admit light from above, and may also 
on some occasions be covered with white linen ; 
they may be opened or closed, according to cir- 
cumstances. 
As the air of the floor-ventilators ascends, and 
that of the ceiling-ventilators descends, according 
to the variations of temperature, it must neces- 
sarily pass through the three rows of wicker trays. 
I have also had six ventilators made in the floor, 
besides those -under the windows, to communi- 
cate with the rooms beneath (^). 
All these ventilators should open easily when 
wanted, as they can alone maintain a constant 
renewal of the exterior air, -without the necessity 
of ever opening the paper window-frames, which 
are within the Italian blinds or shutters. 
I here use thirteen windows (2), three of which 
are placed at one end of the laboratory, while at 
the opposite end there are three doors constructed 
so as to admit more or less air as may be required(a). 
By these doors we are admitted into another hall 
