Page:The history of silk, cotton, linen, wool, and other fibrous substances 2.djvu/163

 *clusion of the sun's rays, another evil is added by the nature of the artificial lights employed, being such as still further to vitiate the air.

An almost incredible quantity of fluid is constantly disengaged by evaporation from the bodies of the insects; and if means be not taken to disperse this as it is produced, another cause of unwholesomeness in the air arises. Noticing this, Count Dandolo observes, "This series of causes of the deterioration of the air which the worms must inhale, may be termed a continual conspiracy against their health and life; and their resisting it, and living throughout shows them to have great strength of constitution."

In seven days from the commencement of the cocoons they are collected in heaps; those which are designed to continue

quantity of vital air necessary to the life of animals, and which they consume by respiration.
 * [Footnote: the leaves of vegetables are struck by the sun's rays, they exhale an immense

"These same leaves in the shade as well as in darkness exhale an immense quantity of mephitic or fixed air, which cannot be inhaled without destruction of life.

"This influence of the sun does not cease even when the leaf has been recently gathered; on the contrary, in darkness, gathered leaves will exhale a still greater quantity of mephitic air.

"Place one ounce of fresh mulberry leaves in a wide-necked bottle of the size of a Paris pint, containing two pounds of liquid; expose this bottle to the sun; about an hour afterwards, according to the intensity of the sun, reverse the bottle and introduce a lighted taper in it; this done, the light will become brighter, whiter, and larger, which proves that the vital air contained in the bottle has increased by that which has disengaged itself from the leaves: to demonstrate this phenomenon more clearly, a taper may be put in a similar bottle, that only contains the air which has entered into it by its being uncorked. Shortly after the first experiment, water will be found in the bottle which contained the mulberry leaves; this water, evaporating from the leaves by means of the heat, hangs on the sides, and runs to the bottom when cooling; the leaves appear more or less withered and dry according to the liquid they have lost. In another similar bottle place an ounce of leaves, and cork it exactly like the former; place it in obscurity, either in a box, or wrap it in cloths, in short, so as totally to exclude light; about two hours after, open the bottle, and put either a lighted taper or a small bird into it; the candle will go out, and the bird will perish, as if they had been plunged into water, which demonstrates that in darkness the leaves have exhaled mephitic air, while in the sun they exhaled vital air".— Treatise on the Art of Rearing Silk-worms, p. 144.]