SILK-WORMS. 
193 
3. An atmosphere vitiated by the fermentation 
of leaves and dirt, or by the later worms that lie 
on the litter, as well as by the defect of circula- 
tion in the interior air, which renders the breath- 
ing of these insects difficult; relaxes their organs, 
and also causes various diseases among them. In 
such cases, many worms drop off, others form 
bad cocoons, die within them when they are 
finished, and are spoiled. 
4. A case of very rare occurrence here, but 
which I shall note, to complete my views on this 
subject, is, too warm and dry an atmosphere, 
which dries up the worms, producing too violent 
a contraction of the shin, not proportioned to the 
vacuum which increases in the animal by the slow 
pouring out of the silky substance, and by tran- 
spiration ; and thus forces them to violent and 
fatiguing action in the formation of the cocoon. 
In which case they empty the reservoirs of silk too 
fast, forcing the silk-drawing tubes, producing 
coarser silk, which thus never can have that 
fineness w r hich it possesses when produced in 
a temperature of 69°. Having tried to ex- 
pose a number of silk-worms to very dry air, 
at 100° of temperature, I obtained from the 
cocoons, by the common method of spinning 
several thousand feet of the coarse downy floss or 
bave, the weight of this floss being six times 
K 
