80 



tore in death U'liipcraliiix's, coukl be iiidueed artilicially 

 l)y exposure of llie animals to cold; changes in cokl resis- 

 tance were caused also by ex)»osui'e to moisture. AVJiile 

 a(|ualic insects consistently showed the same survival 

 temijcratures, insects which could be experimentally de- 

 hydrated presented a considerable lowering of the death 

 point. The Japanese beetle, for example, which can lose 

 half of its body weight in the form of water, exhibiled a 

 lowering of about 28 degrees in its survival tempei'ature, 

 when so dried. Several species of oak borers are self- 

 dehydrating during the winter and show a natural peri- 

 odicity in cold hardiness. Artificial softening, the reverse 

 of artificial hardening, could be accomplished by exposure 

 to high humidity or high temperature. As to the freez- 

 ing points, the author distinguishes two of them, the tirst 

 one being the freezing point of the blood and the second 

 probably that of some tissues, such as nerve tissue, or of 

 some tissue components. The insects were able to recover 

 from exposure to the first freezing temperature but not 

 from exposure to the second. The latter, therefore, 

 might be considered the death temperature. The time 

 factor was found to be important. 



Another significant work along the same line is that 

 of Sacharov (1930). He determined, by the dilatometer 

 method, the quantity of ice formed in the body of insect 

 larvae at various temperatures during hibernation and 

 during the active state, and correlated these data witli 

 cold resistance. He found that, for example, in the 

 active caterpillar of the broioi fail moth, 44.85 per cent 

 of the water-content was frozen at -7.8°, while in the 

 hibernating stage only 5.06 per cent was frozen at - 11.1°, 

 and 15.22 per cent at - 17.35°. The total water-content 

 in the 2 stages was, respectively, 82.94 per cent and 71.83 

 per cent of the body weight. On the other hand, the 

 active caterpillars died after exposure to -7.8° while the 

 hibei'uating ones withstood - 17.35°. Sacharov also thinks 

 that the cold resistance bears some important relation to 

 the fat-content, which was about twice larger in the liiber- 



