lOS 



ELEVENTH REPORT. 



.cloth to .cover the o])en ends and so imprison them, a hook to suspend and 

 agitate the tube in the diluted insecticide, a time piece recording seconds 

 and, finally, clockglasses or petri dishes to confine the insects, if not killed, 

 and to allow frequent examinations. Some commonly used dip should be 

 taken as standard. ]')referably one which has given good results in some 

 certain dilution. Then, various dilutions, such as 1 in 200, 1 in 100, 1 in 50, 

 1 in 30, should be tried by dipping insects enclosed in the glass tubes into the 

 dilutions mentioned, for exactly one minute, and noting that dilution found 

 to be effective in killing the insects. At least three insects should be used 

 for each test and the test should be repeated with the effective and the 

 nearest non-effective dilution at least three times to eliminate errors due 

 to variations in the resistance of the insects. 



COMJ>ARISON OF CREOSOTE OIL DIPS — INSECTICIDAL VALUES. 



Official Dilution: 



No. 1—1 in 76. 

 No. 2—1 in 73. 

 No. 3 — Not permitted in official dipping for sheep scab. 



Insects fairly uniform in size will vary less in resistance than might be 

 expected. Apparently, those which seem to be exceptionally resistant are 

 ones best protected by adhering air bubbles. It is, therefore, necessary to 

 agitate the tube containing the test insects while immersed in the solution 

 to detach these air globules which prevent intimate contact with the in- 

 secticide. 



It is true this method will not detect with exactness the difference betweea 



