SILK-WORMS. 
115 
In this fourth age, as in the fifth, there will 
probably be days in which it will not be possible 
to maintain the temperature of 71°, because of 
the heat of the weather, as the season advances ; 
and in spite of artificial means, it may very pro- 
bably rise to 73° or upwards. 
This augmentation of temperature need create 
no anxiety, because it does no harm. It is suf- 
ficient to prevent the circulation of air being 
interrupted. The moment it is perceived that 
the exterior atmosphere begins to heat the labo- 
ratory, the ventilators should be opened as well 
as all apertures on the side unexposed to the sun. 
I have seen, in the space of two hours, some of 
my laboratories rise from 71° to 80°. I then 
opened all the apertures, and the air being stag- 
nant, I had some faggot-wood burnt in the fire- 
place, placed in the angles (Chap. XIII.) to es- 
tablish a complete current of air, and thus change 
the air of all the rooms thoroughly. If, instead 
of thus acting, when the heat of the season ceases 
suddenly, (which augments the fermentation of 
the litter) we should exclude the exterior air from 
the laboratory, we may chance to lose whole 
broods of silk-worms, because as they grow, the 
mass of leaves and litter increasing, the dampness 
proceeding from it will more quickly produce 
fermentation, the heat would also augment, and 
