SILK-WORMS. 
291 
three rows of wickers, and there will be four 
passages or avenues between these three rows, 
two next the two side walls, and two between 
the wickers. These passages are about three 
feet wide ; they are useful in giving free access to 
the wickers, and for placing the steps and boards. 
There should be posts driven in between the 
wicker trays, which, as I before said, form an 
avenue. On these posts should be fastened little 
bars of wood, horizontally placed, which support 
the wicker hurdles ; there is, between the two 
wicker hurdles, a vacuum of about five inches 
and a half, to allow the air to pass freely, and 
this space corresponds to the size of the vertical 
posts, which form a line at equal distances down 
the laboratory. 
There are in the building thirteen unglazed 
windows, with verandas outside, and with paper 
window-frames inside ; under each window, near 
the floor, ventilators, or square apertures of about 
thirteen inches, that they may be closed by a 
neatly-fitted sliding pannel, so as to enable you, 
at will, to make the air circulate, which, entering 
and issuing, will blow over the whole floor. 
When the air of the windows is not wanted, 
the paper frames may be kept closed. The ve- 
randas, or Italian shutters, may be opened or 
shut, according to circumstances. When the air 
is still, and the temperature of the interior and 
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