324 
THE ART OF REARING 
the hurdles, having only yielded 7451bs. 12oz. of 
dung, including excremental substance, and 1201bs. 
of cocoons, in all making 8651bs. 12oz., there is a 
loss escaped in gas, vapour, and steam, &c., in the 
laboratory, of 4961bs. 4oz. 
5. That three parts nearly of these 4961bs. 4oz. 
of substance having been extracted, as we have 
shewn (in Chap. VIII.), in the last six days of the 
fifth age, it follows, that in those days, the above 
substances weighed daily 30, 40, and 501bs. 
6. That in a laboratory containing the worms 
proceeding from five ounces of eggs, such as we 
have described, there must have escaped on each 
of the last six days of the fifth age, 300 or 4501bs. 
of gas and vapour, invisibly to the eye. 
These latter statements which I mentioned else- 
where, and which would seem incredible were 
they not demonstrated by exact calculation, thus 
connected, present strong evidence of how formi- 
dable the enemies are which assail the laboratory. 
These evils are unknown in the hot climates 
whence originated the silk-worms, because there 
these insects are always in contact with the external 
air, which circulates freely, and dispels gases and 
mephitic vapours. 
Although the cultivators among us know not the 
force of the material cause that'produces the death 
of their silk -worms, they, however, know that in 
