February, '11] SHAFER: IXSECTICIDE EFFECTS 49 



etc., increase the rate of excretion of carbon dioxide in insects. Large 

 amounts of the same substances, as they brought about quiet and death, 

 reduced the output of carbon dioxide. When the output of carbon 

 dioxide was increased, the amount of oxygen used increased; as the 

 output of carbon dioxide decreased, the oxygen used decreased in about 

 the same ratio, until when the insect was deeply under the influence 

 of the insecticide (this was tried out especially with gasoline vapor, 

 hydrocyanic acid gas and nicotine) and nearly dead; then the respira- 

 tory ratio increased. That is, the amount of carbon dioxide given off 

 was greater in proportion to the oxygen used than was normal. 



As evidence that this increase in the respiratory ratio is due to the 

 insecticide, it was shown that death from starvation or from mechani- 

 cal injury causes a decrease in the respiratory ratio. 



Insects confined in pure hydrogen, nitrogen or carbon dioxide, give 

 off carbon dioxide; and the rate of its excretion under this condition, 

 it was found, is often increased by gasohne or by hydrocyanic acid 

 gas — never decreased appreciably, although insects placed in nitrogen 

 for 8 to 10 hours after treatment vnth one of these insecticides, seemed 

 to recover as well as if they had been left in air. Indeed, the chances 

 of recovery of the former often seemed to be better. 



By actual measurement of the gases, it was proven that certain gases 

 and vapors are absorbed into the bodies of insects and that in an 

 atmosphere of pure air, they may be given off again. In case of some 

 gases, their presence in the insect body can be shown by injecting 

 solutions which, upon contact with the gas, give rise to colored pre- 

 cipitates. For example, hydrogen sulphide can be detected in this way 

 by a solution of lead acetate or of cadmium chloride — a black sulphide 

 precipitating in the former and a yellow sulphide in the latter case. 

 The evidence from microscopic sections of insects treated in this way 

 seems to inchcate that some tissues of the insect take up the gases or 

 vapors in greater amounts than others. Moreover, the activities of 

 the insects under the influence of the vapors and gases named,^ — as has 

 already been mentioned, — indicate that the nervous system is espe- 

 cially affected. 



Experiments upon the luminous organs of the larva of Photuris 

 T)ennsylvanica indicate that the light-giving power of these organs is 

 due to an oxidation process, since the light of intact or of excised 

 organs ceases in the absence of oxygen (i. e., in carbon dioxide or in 

 nitrogen) and may begin again when air is admitted. Now it would 

 appear that the presence of carbon disulphide vapor interferes with 

 oxidation in these organs since the luminosity decreases and may even 

 be made to cease when the organs are exposed to a sufficient amount 

 of the vapor. The luminosity may then be made to reappear if the 

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