Page:The history of silk, cotton, linen, wool, and other fibrous substances 2.djvu/146

 that worms which he hatched in May were eleven days old ere they were attacked by their first sickness; others hatched in July were ten days, and those brought forth in August nine days, before they refused their food, preparatory to their first moulting. Eight days appear to be the most usual term for their first attack; and by his judicious treatment count Dandolo shortened even this term by two days. In Europe, except where recourse is had to artificial aid, the term of the caterpillar state is usually that which has been already mentioned.

Sudden transitions from cold to heat, or vice versa, are highly injurious to the silk-worm; but it can bear a very high degree of heat, if uniformly maintained, without sustaining injury. Count Dandolo observed, that "the greater the degree of heat in which it is reared, the more acute are its wants, the more rapid its pleasures, and the shorter its existence." Monsieur Boissier de Sauvagues made many experiments on this point. One year, when by the early appearance of the mulberry leaves, which were developed by the end of April, he was forced to hurry forward the operations of his filature, he raised the heat of the apartment in which the newly-hatched worms were placed to 100°; gradually diminishing this during their first and second ages to 95°. In consequence of the animal excitement thus induced, there elapsed only nine days between the hatching and the second moulting inclusively. It was the general opinion of those cultivators who witnessed the experiment, that the insects would not be able to exist in so intensely heated an atmosphere. The walls of the apartment, and the wicker hurdles on which the worms were placed, could scarcely be touched from the great heat, and yet all the changes and progressions went forward perfectly well, and a most abundant crop of silk was the result.

The same gentleman, on a subsequent occasion, exposed his brood to the temperature of 93° to 95° during their first age; of 89° to 91° in the second age; and remarked that the attendant circumstances were the same as in his former experiment, the changes of the worm being performed in the same space of time; whence he came to the conclusion, that it is not practicable to accelerate their progress beyond a certain point