SILK-WORMS. 
271 
chrysalis. The chemical alterations to which the 
diseased worm and chrysalis are exposed, make 
them lose much weight, as we shall hereafter 
explain. 
The impediment to transpiration, whether gene- 
ral or partial, may occur in divers manners, as 
well as the accumulation of the deteriorating sub- 
stances. 
1. If the worms lie too thick, the transpiration 
is checked in those parts which are in contact. 
2. If the apartments in which the worms are 
reared are not sufficiently airy, as fast as the air 
which is in contact with the body of the worm is 
charged with damp, it becomes less fit for the in- 
sect to breathe, and thus checks transpiration. 
3. By the great atmospheric variations. Great 
heat will promote abundant transpiration ; the 
cold, even when dry, will harden the worm. In 
the first case, most of the parts of the worm ex- 
posed to the air will transpire, while transpira- 
tion will almost cease in the parts in immediate 
contact with other worms. In the other case the 
hardness caused by cold, instantly checks all tran- 
spiration, diminishes the vital strength, and dis- 
poses the acid, earthy and alkaline substances to 
reaction within the insect. 
4. In impeding respiration, silk-worms not pos- 
sessing lungs, breathe, as I before stated (Chap. 
II.), by several apertures placed near the feet. 
