172 
THE ART OF REARING 
have unloaded itself of all the excremental matter 
contained in the intestinal tube. 
It is not only requisite to know the last degree 
of perfection of the worm, to facilitate its means 
of forming the cocoon, but also to know all the 
other operations necessary to ensure the cocoons 
being of a very good quality. 
The cleanliness of the tables, in these last days of 
the fifth age, requires great attention, to preserve 
the health of the silk- worms. 
It is with these insects as wfith all other ani- 
mals, some are quick in all their operations, others 
more slow ; and it is important to form just ob- 
servations on these facts. 
To enable those who rear silk-worms to have 
correct ideas on the necessity of maintaining dry 
and pure air in the laboratory, I will endea- 
vour here to convince them, by evident facts and 
calculations, that although it may appear to 
them that moist vapours and mephitic exhala- 
tions have ceased in the laboratory, it is, on the 
contrary, at this moment, that they prevail in the 
proportion ; and when by vital action, or the disposition of 
the organs, they are balanced and suspended, the chemical 
law of affinity cannot be applied to them. But when these 
substances accumulate for want of care, and vital action di- 
minishes, then, as we may see in Notes 20 and 21, these sub- 
stances will produce re-action in the body of the silk-worm, 
destroy the equilibrium which existed, and produce those 
diseases which are the evident result of chemical action and 
attraction. 
