VI 
PREFACE. 
On reflection, we shall perceive that the 
power inherent in every animal, of destroy- 
ing a certain portion of air, and rendering 
it unfit for the purposes of vitality, be- 
comes dangerous, in proportion as the 
space in which the animal exists is dimi- 
nished. A few hundred Silk-Worms, reared 
in an ordinary room of eight or ten feet 
square, where the air has free egress and 
ingress, possess not the power of vitiating 
the surrounding atmosphere so rapidly, as 
the current carries off the air so vitiated, 
and supplies its place with purer. 
Provided, therefore, attention be paid to 
the temperature, and proper food admi- 
nistered, success under such conditions is 
inevitable. But if the number be in- 
creased to several thousands, the quantity 
of air vitiated in a given time will increase 
in an equal proportion, and as the current 
of air receives little or no accession of ve- 
locity, it will easily be conceived that un- 
less recourse be had to artificial ventila- 
tion, these worms so reared will be coeteris 
paribus, under circumstances far less fa- 
vourable than the former. 
