BY T. HARVEY JOHNSTON AND M. J. BANCROFT. 285 



in the hot diy interior. (See Stewart and others, 1915, 

 pi. I. for tick infested areas of Queensland and N.S. Wales). 

 Altitnde^ — along the coastal belt — has little effect upon 

 the activities of the parasite. On the Atherton tal)leland 

 2,500-3,000 feet above sea level, cattle become tick-infested 

 as they do on the Blackall Range, e.g., at Malen^' and 

 •Crohamhurst. Ticks appear periodically (apparently as 

 reinfestations) on the Springbrook Plateau, but the "\A-inters 

 are too severe to permit the pest establishing itself. 



Effect of Arsenic on Resistance. 



As already mentioned. Mr. Hull claims that if a resist- 

 ant animal be treated with arsenic, either bj' spraAdng, 

 dipping or washing, the resistant condition becomes at least 

 temporarily suppressed and that such animals then carry 

 ticks (R.S.C.. p. 3, 8, 57). 



He informed us (7/6/1915) that he had applied ar.senical 

 solution to a part of the hide of a resistant coav and the 

 part so ti^eated matured abundant ticks while the rest of 

 the skin remained free from them. On another occasion 

 he wrote (20/12/1915) stating that some milking cows were 

 sprayed a few weeks previously and subsequently became 

 tick infested so that spraying was again necessary. At the 

 time drought conditions prevailed locally, food Avas scarce, 

 and those cows which were being milked were in a very poor 

 condition, whilst the drj^ stock, whose condition was much 

 better (since they were not subjected to the task of producing 

 milk), maintained condition and were tick-free. We think 

 that it was the poverty of condition and not the application 

 of dip fluid which brought about a lowering of resistance 

 and permitted tick infestation to occur. 



He believed that there exists just below the skin of 

 resistant cattle some substance which is detrimental (or 

 may we say distasteful) to the tick, l)ut that such substance 

 becomes destroyed by the action of the arsenic absorbed by 

 the skin. 



There is some difference of opinion as to whether arsenic 

 from dip fluids does actually become absorbed. Graybill* 



*Graybill, H. The action of arsenical dips in protecting cattle from 

 infestation witli ticks. U.S.D.A., B.A.I., Bull. 167, 1913, p. 19. 



