144 
THE ART OF REARING 
rish in a moment, and the following is the way it 
may happen. 
If the smoke is caused by the exterior air forci- 
bly driving it down the chimney into the labora- 
tory, and if this air, already mephitic, is heated in 
driving down the chimney by the fire, it may, if 
it is not quickly expelled, occasion the instant 
suffocation and death of the silk-worms, particu- 
larly should there hang any damp about the labo- 
ratory, which is unluckily too frequently the case. 
Another cause of the corruption of the air in 
the laboratories, is the darkness in which they are 
generally kept ; the greater the obscurity the 
greater the exhalation of deadly air from the 
leaves of the mulberry, as would equally be the 
case from any other vegetable. 
Should no other inconvenience result from keep- 
ing silk-worms exposed to the sun while feeding, 
they would have the advantage of being in the 
midst of vital air; because the leaves, which, when 
in darkness, exhale a deadly gas, would in the sun 
send forth the purest possible air, until the leaves 
were dry or consumed *. 
To the harm caused by darkness in a laboratory 
as it vitiates the air, may be added that produced 
by the artificial lights employed in them. This 
* There is in the order of nature, a certain and very sur- 
prising fact • when the leaves of vegetables are struck bv the 
