274 
THE ART OF REARING 
form a perfect chrysalis. I have, by this treat- 
ment, got numbers of good and tolerable cocoons. 
It was, therefore, evidently necessary, to cure these 
worms, that they should be sheltered from any 
agitation of the air, that they should be warmed, 
and placed in dry air ; to conquer the excessive 
moisture which penetrated them. When damp, 
heat, corrupt air, fermented litter, and stagnant 
air, act at once on the silk-worms, it is evident 
that suffocation may at any time take place, and 
speedily annihilate their vitality. 
from which it derives its name, in the urine of man, which 
contains urea, and in urinary calculi. 
Having discovered this acid in the moths of the silk- 
worm, it might be found in other insects. The solution of 
the following problem might also be found. How is it that 
a quantity of this peculiar acid is found in the guano ; an 
earthy substance which exists in various places, and on some 
of the various coasts of Peru, and which has been used as 
manure for a great series of time to the inhabitants of that 
country? It would then be found that guano is produced 
by the decay of an enormous quantity of insects, or of 
substance deposited during a long series of ages, by in- 
sects, particularly as it is known that the guano is found in 
a layer on granite, as ancient as the creation of the 
world. The other substances which compose guano are 
analogous to those contained in the earthy substance depo- 
sited by the moths of the silk-worm. 
To return to our subject, it appears that there is always a 
certain portion of earthy acid and saline substance retained 
in the body of the silk-worm, even in a healthy state, which 
when augmented by ill-management must produce in the in- 
sect that scries of chemical attractions of which we have 
spoken above. 
