December, '12] HOLLOWAY: POISON EXPONENT 455 



tions being equal. But to say that Arsenate of Iron Grasselli is there- 

 fore worth only half the market price of Paris Green is to make a state- 

 ment that may or may not be true. Factors other than the Poison 

 Exponent are to be considered in determining the market value of a 

 poison. 



Second instar: The larva subjected to Arsenate of Iron died within 

 6 hours, while the larva subjected to Paris Green died within 2 hours. 

 Poison Exponent = 2-6 = .333 + . 



Third instar: The larva subjected to Arsenate of Iron died within 

 27 hours, while the larva subjected to Paris Green died within 22 hours. 

 Poison Exponent = .81 + . 



Fourth, fifth and sixth instars: The larva subjected to Arsenate of 

 Iron died within 46 hours, while the larva subjected to Paris Green 

 died within 22 hours. The Poison Exponent for each of these instars 

 is .47 + . Attention is called to the fact that observations were made 

 bi-hourly through the day from eight or nine in the morning till five 

 or six in the evening. When larvse died during the night the deaths 

 were not recorded until the next morning. The larvse of all the in- 

 stars but the first and second died during the night, with one excep- 

 tion, so that the Poison Exponents for the larger instars are most prob- 

 ably not correct.. In future work it will be necessary to make obser- 

 vations at bi-hourly intervals continuously until the deaths of the 

 larvae. In order to obtain correct Poison Exponents it will also un- 

 doubtedly be necessary to make many duplicate experiments and take 

 the average of the results obtained for any one exponent. This 

 probable necessity arises from the fact that conditions for work are 

 seldom ideal and that mistakes and incorrect interpretations will be 

 made. The average of a large number of results will tend to obviate 

 the discrepancies of a few of them. 



Larvse of Heliothis were not found after these preliminary experi- 

 ments were made, and as other work was more pressing the greater 

 number of the outlined experiments were not conducted. If they had 

 been carried out as planned, however, the necessity for continuous 

 observations would have rendered many if not all of the results value- 

 less, as the services of no one were available for the night observations. 



As to the economic benefit to be derived from the application of 

 the Poison Exponent, we can only try to imagine what might occur 

 if it came into use. Many new chemicals have been put on the market 

 within the last few years, and the properties of the greater number of 

 them are probably unfamiliar to most entomologists. The Poison 

 Exponents of these chemicals for a number of species could be ascer- 

 tained in a comparatively few months, while years would be consumed 

 if the new poisons were to become known in the slow process of unre- 



