SILK-WORMS. 
143 
and, by merely reducing it to vapour, does not 
render it so noxious as the elements of which it is 
composed. 
From what I have stated, the cultivators, some- 
times seeing their silk-worms after these operations 
more stimulated, have decided that the means em- 
ployed were useful remedies, ignorant that the 
apparent advantages proceeded from other causes. 
At all events it is a clear fact, that perfumes tend 
to corrupt the air ; besides, when a laboratory is 
carefully attended, it will always offer a pleasant 
smell exhaled by the leaves, and need no better 
perfume, than that it should be well kept. 
I should here speak of the harm which may be 
done by the smoke of chimneys, which spreads often 
through the laboratory, and remains stagnant in 
it. When this happens, it is caused either by the 
ill construction of the chimneys, or want of care in 
the laboratory. It may be, that the smoke is the 
effect of some impediment between the exterior 
and interior air, and may prove injurious to the 
worms ; although sometimes this impediment, by 
producing agitation in the interior air, may in 
some degree have its use, without those who 
have the care of the silk-worms being able to solve 
the question. Yet is it very certain that if the 
smoke often infests the apartment, it is to be feared 
we may see all the silk-worms of a laboratory pe- 
