SILK-WORMS. 
181 
with mulberries, and consist of coarse and woody 
substance, which they cannot eat. 
During the time of this operation, the exterior 
air should be freely admitted on all sides, and 
may be drawn in by lighting a blazing light fire 
in the grate. 
All the ventilators should be open, as well as 
the doors and windows ; if there is no w r ind, and 
if the weather is not much below the 68th de- 
gree of temperature, which is the prescribed heat 
of the laboratory. Although generally the air, 
at this time of the year, is neither cold nor windy 
enough to be obliged to shut up the laboratory, 
it has happened to me to be obliged to take great 
precaution in admitting air. In June, 1813, the 
exterior air was at 53°. The unfavourableness of 
the weather lasted long, and rain and wind were 
continual ; and I was obliged to be careful, even 
in opening the ventilators. 
In such cases, a part only of the ventilators 
should be opened at once. Light fires should be 
lighted in the fire-places, and obtain thus a free 
circulation of air, gentle and steady, without 
cold, and getting rid of a good deal of damp, 
which improves the silk- worms, and enables them 
to breathe more freely. The fumigating bottle 
should also be passed once or twice through the 
laboratory, and the hygrometer will shew whe- 
ther the air is grown sufficiently dry. 
