OF PAPILIONACEOUS INSECTS. 49 



" I subjected eggs of several insects to a more 

 severe trial than in the winter of 1709. Among 

 others were those of the Silk-worm Moth, and the 

 Elm Butterfly, which I enclosed in a glass vessel, 

 and buried five hours in a mixture of the ice and 

 rock salt, when the thermometer fell six degrees 

 below zero ; notwithstanding which caterpillars were 

 extruded from all the eggs, and exactly at the same 

 time with those which had not been subjected to this 

 experiment. In the succeeding year, I exposed them 

 to a still greater degree of cold. I prepared a 

 mixture of rock salt and nitrate of ammonia, and 

 reduced the thermometer to twenty-two degrees 

 below zero, which was twenty-three degrees lower 

 than the cold of 1709. They suffered nothing from 

 this rigorous treatment, as they were hatched in due 

 season. 



" From these combined facts we must conclude, that 

 cold is less prejudicial to germs and eggs than to 

 animalcula and insects. In general, it is found that 

 germs can survive the cold of two degrees below 

 zero ; while it is known that some animalcula die at 

 the freezing point, and others at about twenty degrees. 

 The eggs of various insects are productive after 

 being exposed to a temperature of twenty-two degrees 

 below zero, while insects themselves die at sixteen 

 and fourteen degrees. This I have proved in the 

 eggs of the Silk-worm Moth, and of the Elm 

 Butterfly; and although I ascertained that some 

 insects can stand a great degree of cold, I have 

 invariably found it to be in a much less ratio than 



