The Chinese calculate that the same number of insects which would, if they had attained the full size in twenty-three or twenty-four days, produce twenty-five ounces of silk, would give only twenty ounces if their growth occupied twenty-eight days, and only ten ounces if forty days. In order, therefore, to accelerate their growth, they supply them with fresh food every half-hour during the first day of their existence, and then gradually reduce the number of meals as the worms grow older. It deserves to be remarked as a fact unnoticed in Natural Theology, that the substance on which this valuable caterpillar feeds, is the leaf of the mulberry-tree; and Providence, as if to ensure the continuance of this useful species, has so ordained it that no other insect will partake of the same food; thus ensuring a certain supply for the little spinster. Many persons believe that light is injurious to silk-worms; but, so far from this opinion being correct, the opposite belief would probably be nearer to the truth. In its native state, the insect is of course exposed to light, and suffers no inconvenience on that account; and it has been observed by one who gave much attention to the subject (Count Dandolo), that in his establishment, “on the side on which the sun shone directly on the hurdles, the silk-worms were stronger and more numerous than in those places where the edge of the wicker hurdle formed a shade.” The obscurity wherein the apartments are usually kept has a very pernicious influence on the air: the food of the worms emits in light oxygen, or vital air, while in darkness it exhales carbonic acid gas, unfit for respiration. This well-known fact occurs alike with all leaves similarly circumstanced[138]. To the bad effects thus arising from the exclusion 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. [138] “There is in the order of nature a certain, and very surprising fact; when the leaves of vegetables are struck by the sun’s rays, they exhale an immense quantity of vital air necessary to the life of animals, and which they consume by respiration. “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.