SILK-WORMS. 
125 
In the seven days of the fourth age, the worms 
which were before about one inch long have grown 
half an inch in length. In this age, their weight 
is augmented fourfold. 
After the third moulting, 144 insects weighed 
one ounce : it now requires only 35 to make up 
the ounce. 
After this moulting they are of a darker co- 
lour, greyish, with a red cast. 
During this age, shavings of wood should be 
burnt in the corner fire-places, three or four times 
a day; dry straw will answer the purpose also, as 
this is done to renew and lighten the air of the 
room, without particularly heating it. Should 
it be necessary to heat the laboratory, that should 
be done either with the stove, or by burning large 
wood in the fire-places. 
When straw or shavings are burnt, the ventila- 
tors should be opened for the circulation of the air. 
If the exterior temperature be not cold, and 
should be without wind, the doors and window 
may also be opened ; when the interior tempe- 
rature, by these means, is lowered half a degree, 
the windows and doors should again be closed, 
leaving the ventilators open, and the temperature 
will rise again. 
Those who have, instead of shutters, Venetian 
blinds to the windows, or bars, should open the 
windows, to allow the air to enter. 
