BY T. HARVEY JOHNSTON AND M. J. BANCROFT. 241 



(3) To ascertain whether the exudation mentioned by- 

 Mr. Hull is or is not merely that from an ordinary 

 tick sore ; the relation, if any, of the exudation 

 to tick infestation, climate, etc.; effect of dipping. 



Does tick resistance actually occur ? 



We \\i\\'e already brought forward evidence, when 

 dealing \vith. tick wony, that a certain degree of resistance 

 is by no means uncommonly met with amongst cattle. 



We propose firstly to examine the evidence available 

 in regard to Mr. HuU"s animals, viz., that collected by 

 Messrs. Hull, Pound, Corser, Walker, ourselves and others 

 who have had actual experience with such cattle ; secondly 

 the experience of other Queensland farmers and dairymen 

 in regard to tick resistance. 



Tick resistance might be manifested by — 



(a) A failure to develop ticks or a particular species 

 of ticks- — really a tick immunity ; 



(6) A tendency towards light infestation when ordinary 

 controls become heavily infested ; 



(c) A failure of female ticks to become fully matured 

 [i.e. engorged) in such numbers as on controls 

 under the same conditions of climate ; 



{d) A failure of such engorged ticks either to lay a 

 normal number of eggs or to lay eggs showing a 

 normal percentage of hatchings. 



(a) We know there are many ticks which have very 

 limited host relationships, e.g., the cattle tick, Boophilus 

 annulatus, with its several varieties or related species, 

 including the Queensland cattle tick, B. australis, which is 

 occasionally found in horses and sheep. Certain others 

 prefer a particular host species but are not uncommonly 

 found on other hosts, e.g., some species of Argas, Ixodes, 

 etc ; while certain others prefer a particular class of animals 

 and occur only rarely outside that class, e.g., Aponomma 

 (on reptiles)— Still others seem to be indifferent as to the 

 host, so long as it is an amniote vertebrate, e.g., some of 

 our Australian ticks, Some genera are practical^ restricted 

 to certain classes of vertebrates, e.g., many of those maturing 



Q 



