-7- 
MacLeod also referred to the introduction of Toowdered derris root to 
veterinary practice as an acaricide by J. Russell Greig in 1924. 
In 1938 MacLeod (96) discussed the sheer tick and its control in Great 
Britain. He suggested that in cases where ordinary sheep—farming methods are 
not practised end the primary consideration is the removal of the ticks, the 
sheep . should be dipped at short intervals throughout the tick season (mid- 
March to the end of May) in a derris wash, or in some other preparation that 
may he used repeatedly; without harming them. On sheep farms, where it is 
desirable to increase the farm profits without interfering too greatly with 
the normal sequence of farming activities, especially during the "busy lambing 
season, which coincides with the tick season, it is .'suggested that the sheep 
be dipped in one of the snecial -preparations now available that "ill protect 
them from reinfestation for 2 to 3 weeks after its application. The two main 
dippings (one of which is carried out • immediately, before lambing begins and 
the other about 3 weeks later) may be augmented by : one or two supplementary 
dippings* For farms where profitable farming is impossible unless ticks are 
eradicated, s scheme combining starvation of the- ticks with serial dipping of 
the sheep is recommended. 
The North East of Scotland Sheep Tick Committee ( 114) ' in 1939 published 
a. report of work by Walter Moore, of the North of . Scotland 'College "of Agri- 
culture, in 1938 to control the sheep tick. Various standard sheep dips pre- 
scribed for sheep scab ^ere tried but none proved to be completely effective. 
Most of the dips killed the active feeding • stages of the tick, but all failed 
to kill the ticks that had completed feeding, and also failed to protect the 
sheep from reinfestation for more than 1 or 2 days, laboratory tests with 
various insecticides showed that the contact insecticides were very efficient, 
and of the materials tested derris and pyrethrum gave the most promising 
results. In conjunction with the Cooper Technical. Bureau, a large-scale field 
experiment was carried out with a derris din and proved very successful, giving 
a 100-percent kill at all stages. A 1:500 solution of D erris elliptica root 
containing 5 percent of rotenone in water -was found to be most efficient and 
economical. The time of immersing the sheep in the dip bath was found to have 
an important effect on the protective period. In dipping it is not sufficient 
to kill only the ticks on the sheep, as this would necessitate repeated appli- 
cation every 10 days. Enough of the insecticide must be retained on the skin 
or wool to kill all ticks that attack the animal for several days after dipping. 
If sheep are immersed in the dipping solution for at least 30 seconds there is 
a protective period, of from 9 to 10 days during ^hich the animal remains tick- 
-free. Immersion for 1 minute is recommended. 
Cameron (39) in 1939 wrote that in Scotland dipping is used to control the 
sheep tick. In recent years derris has assumed prominence es en acericide 
because of its rapid lethal action and is included in certain proprietary dips, 
along with either arsenic or carbolic, or both. The percentage of derris in 
the bath is about 0.014 of the total extract. Although arsenic alone as an 
ingredient of dir/ning fluids is effective as an acaricide, its efficacy is 
increased when it is combined with carbolic acid, which by itself has only 
very slight toxicity to ticks. Derris alone is quick in its action, but it is 
