98 NATURAL HISTORY. [CH. V. 



I add one premonition to those less experienced 

 gardeners who frequently expose their orange and 

 light tender furniture trees of the greenhouse too 

 early that the first leaves putting forth of this wise 

 tree (sapientissima, as Pliny calls it), is a more in- 

 fallible note when those delicate plants may be 

 safely brought out to the air than any other prog- 

 nostic or indication." 



The rearing of the silkworm requires not only 

 great caution, but great art. The laboratory des- 

 tined to preserve these useful insects, from the time 

 of hatching to the period of maturity, should not 

 be built in the vicinity of any damp spot, or near 

 large rivers or masses of stagnant waters. 



It has been remarked, that a free circulation of 

 dry air is the most favourable to the health of the 

 silkworm; hence, the silkworms in laboratories 

 which are situated on gentle elevations yield a more 

 abundant and a finer harvest of silk than those 

 which are reared on the plains. The laboratory 

 should be placed north and south, in such a way 

 that the largest side should look eastward. A due 

 temperature, proper ventilation, and light, are so 

 absolutely essential to the health of the worm, and 

 therefore to the quality and quantity of silk, that no 

 other apology than the importance of the subject 

 will be needed for enlarging on each of these three 

 heads. 



Heat. It is clear that the hatching of the worm 

 should be adapted to the budding of the leaf on 

 which it is to be fed, otherwise the animal would be 

 produced only to die. Temperature is the mean by 

 which the insect may be retarded or advanced in its 

 development, so as to time its birth precisely to the 

 period of the production of the mulberry leaf. If 

 it be considered that the foliation of trees varies 

 sometimes during many days in the same season 

 of different years, the importance of ascertaining 

 the precise, degree of heat necessary to hatch the 



