102 NATURAL HISTORY. [CH. V. 



overcoming' an atmosphere. The walls, wicker 

 hurdles, were so heated, they could scarcely be 

 touched. All thought they mn|t be burnt — must 

 perish ; however, all went on perfectly well, and, to 

 their great surprise, I had a most abundant crop. I 

 afterward tried giving the silkworms, in their first 

 age, from 93° to 95° ; 89« to 91" in the second age ; 

 and it is remarkable, that the duration of these two 

 ages was nearly similar to that of the preceding 

 experiment, in which they had experienced some 

 degrees more of heat. Perhaps there may be a 

 degree of heat beyond which we cannot affect the 

 progress of the silkworm. It is to be added, they 

 had an equal proportion of food in both experiments 

 to that which is given in the common manner of 

 rearing silkworms. It is singular that these worms, 

 thus hastened in their two first stages, consume 

 only five days in moulting the third and fourth time, 

 although with only a temperature of 82" ; while 

 those worms that have not been hastened, take seven 

 or eight days for each of the two last moultings, in 

 an exactly similar degree of temperature. It ap- 

 pears sufi^cient to have given the constitution of 

 the insects an impetus to regulate the quick suc- 

 cession of its changes. 



" This impetus, which we have been describing 

 as operating such rapid growth, also gives the in- 

 sects vigour and activity, which they preserve 

 through their after ages, and prevents diseases ; 

 thus the hastened and forced cultivation presents 

 a double advantage. It also shortens the care and 

 attendance necessary for silkworms, and sooner 

 ends the anxiety of the cultivator, who must neces- 

 sarily feel anxiety until the cocoon is gathered. 



" To follow this method, it is requisite well to 

 observe the advancement of the season; the shoot- 

 ing of the mulberry leaf ; whether it is checked by 

 cold ; if, again, the grov.'th of the leaf is delayed, 

 and heat should soon after set in, and ripen it more 



