328 
THE ART OF REARING 
laboratory, and may weaken them so as to cause 
their speedy destruction. 
These enemies are — 
1st. The incredible quantity of fluid disengaged 
every day from the body of the insects, by transpi- 
ration and evaporation of the leaves given to them. 
(Chap. XIV.) 
2nd. The deadly and mephitic emanations emit- 
ted every day from the insect, from their excre- 
ments, from the leaves, and the remains of the 
leaves *. 
* It is surprising - to find how large a portion of mephitical, 
consequently deadly, air disengages itself, particularly in the 
fifth age, from the silk-worms, in a laboratory spacious enough 
to contain the worms proceeding from an ounce of eggs. 
If one ounce of the dung taken from the wicker trays, be 
put into a bottle that can hold one pound and a half ofliquid, 
and hermetically corked ; in six or eight hours after, according 
to the temperature, the atmospherical air in the bottle will be 
found vitiated, and totally poisonous. 
To certify which, a bird may be put into the bottle when it 
is first opened ; it will faint and die, if left in it many moments. 
Or if a lighted candle be introduced into it, the candle will go 
out directly. These phenomena would not occur if the bottle 
contained atmospherical air alone. 
From this it is evident that in the fifth age, the laboratory 
before mentioned contains 1200 pounds of dung, which quan- 
tity may corrupt, about every eight hours, a volume of air, 
equal to 16.S00 Paris pints, or bottles, that arc equal to hold 
two pounds liquid ; and in one day this quantity of dung would 
corrupt a volume of air of 50,400 Paris pints. 
Having thus stated the quantity of corrupt air produced by 
the dung in the laboratory, it must appear evident how ne- 
cessary it is to get rid of it, as soon as it disengages itself, and 
continually and gently to renovate the atmosphere. 
