286 A TICK-RESISTANT CONDITION IN CATTLE. 



thought it possible that certain of the ticks used by him in 

 some of his experiments were affected by arsenic absorbed 

 by the skin. Brunnich and Smith* believe that the poison 

 enters the tick partly through its own skin and partly 

 through the 'host tissues, i.e., that absorption of arsenic 

 by the skin of cattle actuallj* occurs. Watkins-Pitchfordf 

 has shown that the poisonous effect of arsenic on ticks 

 though quite local, is not due merely to a deposition of 

 arsenic on the surface of the skin, since if a patch of skin of a 

 habituated animal be closely shaved and carefully washed 

 free of all deposited arsenic, together with the ha.ir and 

 surface epithelium, ticks subsequently applied die just 

 as if such precautions had not been taken. He also found 

 that ticks placed on an animal after dipping, died. Cooper 

 and Laws J confirmed the latter observation, and have 

 stated that experimental inquiry tends to prove that the 

 poison is imbibed by the tick while feeding on its host. 



They endeavoured to answer the question as to whether 

 the tick takes up arsenic from the blood or from the skin 

 of the dipped host, and found that neither the feeding of 

 arsenic to such cattle nor the subcutaneous injection of the 

 poison into the blood stream caused the death of ticks. 

 Consequently ticks did not take up a lethal dose from the 

 host's blood** though the blood may contain enough 

 arsenic to exert a toxic action on hsemoprotozoaff. '' The 

 epidermal cells possess a special affinitj^ for arsenic and once 

 this arsenophile proclivity is satisfied, the excess of arsenic 

 is available for absorption by the blood. It is obvious 

 that the total amount of arsenic in the general blood 

 sj'stem cannot be vevy great since the general health of the 

 animal is not interfered with in any way. But a consider- 

 ation of the amount of arsenic applied every w^eek {i.e., in 

 regular dipping) .... and especially the appearance 



*Brminich and Smith. Factors influencing efficacy and deterioration 

 of cattle-dipping fluids. Q'land Agric. JOur., 1914, pp. 81-92. 



fAn illustrated pamphlet on tick destruction, etc. (p. 50), 1911, 

 Maritzburg, quoted hy Cooj^er and Laws. Some obsenrations on the 

 theory and practice of dipping. Parasitolog}', 8, 1915, pp. 190-217 (p. 19G). 



JCooper and Laws, l.r., p. 196-7. 



**Cooper and Laws, I.e., p. 199 



IfCooper and Laws, I.e., p. 202, 203. 



