SILK-WORMS. 
195 
sistency; the silk-worm lias then cast its envelope, 
is changed into the chrysalis, and has entered its 
sixth age. 
7. Quantity of Vapour, Gas, and Excremental 
Substance, emitted by the Silk-worm, from the 
time it reached its highest point of Growth, un- 
til it has reached maturity , and until the perfect 
formation of the Cocoon. 
I here offer the calculation resulting from facts, 
by which I have been able to ascertain the quan- 
tity of substance which issues from the silk-worm 
towards the close of the fifth age : that this calcu- 
lation may shew the evils which are constantly 
likely to attack a laboratory. 
It must be well observed, that I only allude to 
the noxious emanations exhaled by the silk-worms, 
and not of the leaves, fibrous fragments, and ex- 
crements, all which substances deteriorate the air, 
and are injurious to the silk-worms, if not speedily 
removed; of these I shall speak separately. (Chap. 
XIV.) 
The result of my experiments proves, that 360 
silkworms, which produce about one pound and a 
half of cocoons, weigh, when at their highest 
growth and size, three pounds, three ounces and a 
half. 
The silk-worms, after this, are ready to begin 
their cocoons, in the course of two or three days, 
K 
