CH. V.] HISTORY OF SILK, ETC. 101 



siderable it may be. Native of Asia, it must be 

 accustomed to heat more intense than it can expe- 

 rience in Europe ; but the sudden change from 

 moderate heat to violent heat it cannot bear. Rapid 

 changes in general from heat to cold and cold to 

 heat, are highly injurious. In its native climate it 

 is not exposed to these vicissitudes, and therefore 

 thrives well without requiring all the care we are 

 obliged to bestow on it. With us, on the contrary, 

 the temperature of the atmosphere is so variable, 

 that without artificial means we could not fix it in 

 our laboratories for rearing silkworms. A series 

 of experiments has proved, that in France, 68 is the 

 most suitable to the silkworm. Some cultivators 

 have raised it as high as 73 and even 77 with good 

 success. We must not lose sight of this fact, that 

 it is not heat that affects the silkworm, but sudden 

 transitions from one temperature to another, such 

 as making it pass from 68 to 77 in one day, I am 

 convinced would greatly annoy it, and injure its 

 health. If it happen to be necessary to hasten the 

 worms in consequence of the advanced state of the 

 mulberry leaf, which cannot be retarded, it should 

 be done gradually, so that they perceive not the 

 alteration. The silkworm suffers as much from dif- 

 ficulty of breathing in bad air, as from sudden 

 changes of temperature. M. Boissier de Sauvagues 

 will show us, by his experiments, to what degree 

 the heat may be raised in rearing silkworms, with- 

 out fear of injuring them. One year, when hurried 

 by the early growth of the mulberry leaves, which 

 were developed towards the latter end of April, I 

 gave the silkworms 100 of heat during the two 

 first days after hatching, and about 95 during the 

 remainder of the first and second age. There 

 elapsed only nine days from the hatching until the 

 second moulting or casting, inclusively. Those 

 who saw the process could not imagine that silk- 

 worms would be able to stand so intensely hot and 

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