MICHIGAN ACADEMY OF SCIENCE. 1C9 



two dips which differ only by 10% in the amount of oil contained in an 

 emulsifiable form, but it will determine that dips differ in efficiency and that 

 this difference is not due to the amount of oil contained, so much as to the 

 character of the oil and to the manner of its coml3ination. 



When a creosote oil dip in a dilution of 1 in 250 of water will effectually 

 eradicate sheep scab from a flock badly infected, and is of such a composition 

 as not to come within the ruling and approval of the government experts, 

 they have evidently overlooked the important points of this class of insecti- 

 cides. 



By the process of assay described, this very efhcient dip (Xo. 3) would have 

 been found to contain resin, alkali, water and creosote oil in almost the 

 same proportions as the average clip on the market, but deficient in the ingre- 

 dient which is considered of utmost importance. For this reason, it would 

 probably not l)e permitted for use in any official dipping for scab. 



No satisfactory information has been obtained on the points as to exactly 

 how these insecticides act and why the physical condition of their dilutions, 

 if it be physical, makes them so efficient. While these questions are un- 

 answered and a rational chemical method is, therefore, not possible, these 

 products evidently should l)e classed with those requiring a biological stand- 

 ardization. Such a method is recjuired for serums, vaccines and some 

 im]:)ortant animal and vegetable extracts of which even more is known 

 chemically than is known of creosote oil. It is, therefore, reasonable to 

 suggest that until there is more definite information on the points in question 

 a similar method of valuation should be applied to this most important 

 class of insecticides. 



Detroit, Michigan, April 20, 1909. 



♦Presented before the Section of Entomology at the Boston meeting of the International Cong.ess 

 of Zoologists, June, 19.6. 



