Xew York Agricultural Experiment Station. 351 



merits. 12 Hydrocyanic acid gas differs from oxygen in its strong 

 affinity for water and greater solubility. Briefly, the amount of gas 

 that an insect can take into its tissues in a given time depends upon 

 the movement of gas through the spiracles and the condition of the 

 tracheal wall with reference to moisture. 



Temperature. — Changes in temperature very probably affect the 

 hibernating animal in several ways, but of most importance in this 

 connection is the rate of metabolism and the resulting reflex move- 

 ments. With many species of animals and plants the effect of 

 temperature changes has been observed. 13 It has been found that a 

 rise in temperature is accompanied by an increase in the rate of 

 respiration. It continues to increase as the temperature rises, until 

 the injurious action of the high temperature becomes manifested by a 

 decrease in the respiratory activity. This change in the rate of func- 

 tion of the protoplasm certainly has some bearing on the quickness 

 of action of the gas but is probably not so important in affecting the 

 action of the poison as are the reflex movements that result from the 

 increase in temperature. The caterpillar has no breathing apparatus 

 other than the bellows-like movement of the segments. As long as 

 the caterpillar was quiet the gas could only enter by diffusion, but 

 when the caterpillar begins to crawl there is a pumping action that 

 greatly hastens the movement of the gas. The supply of cater- 

 pillars used in these experiments was kept at a temperature of thirty- 

 five to forty-five degrees. While the insects were held at a low tem- 

 perature they remained quiet, but when raised to seventy degrees or 

 higher they were stimulated to crawl. It appeared in these experi- 

 ments that much of the difference in the results of the work at dif- 

 ferent temperatures was due to the movements of the caterpillars. 



Moisture. — Changes in the moisture content of plants and lower 

 animals are correlated with changes in the rate of metabolism. This 

 is very evident in seeds, and Kolkwitz 14 has shown that proportional 

 amounts of carbon dioxide are excreted by seeds having different 

 amounts of moisture. With certain low forms of animal life, such 

 as rotifers, tardigrades and nematodes, continued loss of moisture 

 produces a desiccation-rigor, during which metabolism proceeds at a 

 very low rate. 15 As mentioned above, the phenomena of hibernation 

 of insects, which is a condition of reduced activity, have been 

 observed in some species to be accompanied by a relatively low mois- 

 ture content. If an insect is placed in dry air it will lose moisture, 16 

 and we have determined that a fly pupa will absorb or lose moisture, 

 depending upon its water content and the humidity of the surround- 



12 Sharp, David. Cambridge Nat. Hist. Vol. V, p. 130. 

 "Davenport, C. B. Experimental Morphologv- Part I, p. 225. 1897. 

 "Jost. Plant Physiology, Ox. Ed. p. 341. 1907. 



"Davenport, C. B. "Experimental Morphology. Part I, p. 60. 1897. 

 16 Bachmetje\\i, P. Experimental Entomologische Studien. Zweiter Band. pp. 53- 

 61. 1907. 



