W. F. Cooper and H. E. Laws 
197 
Experimental inquiry therefore tends to prove that the poison is 
imbibed by the tick while feeding on the host. 
The fact that engorged females are rendered infertile by mere 
immersion in the clipping-fluid can have little effect in actual practice, 
inasmuch as real success is only attained by killing the ticks before 
they can lay; if the ticks do not die, it indicates a deficiency on the 
part of the dipping-fluid. 
The Effect of an Emulsion in a Dipping-Fluid. 
It was found in the course of our investigations that, to obtain the 
same killing effect, a plain solution of sodium arsenite must be more 
concentrated than a solution to which an emulsion of soap and oil, or 
even soap alone, has been added. 
The method followed was to record by means of diagrams the numbers 
and situations of the ticks on several head of cattle. The animals 
were then dipped in the various solutions which it was decided to test 
and the effect on the ticks noted. Bont ( Amblyomma hebraeum), 
Blue ( Boophilus decoloratus) and Red ticks ( Rhipicephalus evertsi) were 
present. 
It was found that a solution of sodium arsenite containing only 
0-153 per cent, of As 2 0 3 , but to which sufficient emulsion had been 
added, was as efficient as a plain solution, i.e. a solution containing no 
emulsion—containing 0-225 per cent, of As 2 0 3 . 
Watkins-Pitchford (1911a, p. 31) showed that sodium arsenite alone, 
at a strength sufficient to kill the ticks, scalded the cattle. On reducing 
the amount of arsenic, the dip failed to kill the ticks, but by adding a 
paraffin and soap emulsion to the more dilute solution, the ticks were 
destroyed without injury to the cattle (see Appendix II). 
It may be pointed out that the Department of Agriculture of the 
Queensland Government attribute great importance to the presence of 
an emulsion in a dipping-fluid, in that they give official recognition 
only to such dips as contain an emulsion. 
It might be supposed that the increased killing effect of emulsion 
dips is due solely to the presence of soap in the emulsion, but we have 
found that a similar increased effect is obtained by the addition of an 
emulsion of glue and oil. Preparations containing emulsified oil in a 
state of fine division are all characterised by their high wetting power, 
whether the emulsifying agent is soap, glue or some other compound. 
It is probable, therefore, that the increased killing power in both cases 
Parasitology vm 
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