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THE AMERICAN NATURALIST [Vol. XL VII 



to keep out moisture, and the whole was then fastened outside a 

 laboratory window, in such a manner that the bottom rested upon 

 a concrete slab, but the remainder of the jar was not in contact 

 with the laboratory walls. The experiment ran from December 

 28, 1912, to March 9, 1913. 



Unfortunately for this experiment, the winter at Cold Spring 

 Harbor was unusually mild and the minimum temperature re- 

 corded in the jar was only — 10° C. with a maximum of + 11°. 



The jar was then taken into the laboratory and after standing 

 at room temperature for 24 hours a count was made. A second 

 count was made six days later with the results given below. 



Experiments with Carbon Dioxide 

 In the third set of experiments, the influence of carbon dioxide 

 on the differential mortality, approximately 75 larvae of each 

 species were placed in each of three gas wash bottles (E. & A. 

 No. 3,658). The wash bottles were connected together with rub- 

 ber tubing and carbon dioxide from a Kipp generator (lime- 

 stone and hydrochloric acid) was slowly passed through the 

 apparatus during the entire course of the experiment. The car- 

 bon dioxide was first washed through a saturated solution of 

 sodium bicarbonate and then through distilled water before pass- 

 ing to the bottles containing the larva?. 2 



The stream of carbon dioxide was started at 12 m., December 

 19. At 12:05 p.m. the jar nearest the generator (Jar No. 1) 

 showed no movement of T. molitor but the T. obscuris were still 

 very active; at 12:07 p.m. only a few T. obscuris were moving in 

 jar No. 1 and nearly all of the T. molitor in jar No. 2 were dor- 

 mant ; at 12 :09 all of the T. molitor in each of the three jars were 

 in a state of "suspended animation" but a few T. obscuris were 

 3 1 have already shown (J. Biol. Chem., 10, p. 90, and Amer. Nat., 45, 

 pp. 749-750) that it is possible to keep insects in pure carbon dioxide for 

 hours without causing death, although to all appearances they are dead 

 within a very few minutes after being subjected to the action of the gas. 



