BY T. HARVEY JOHNSTON AND M. J. BANCROFT. 313 



in the narrow circle about the puncture is found to be densely 

 packed with infiltrated cells." This '" sticky accumu- 

 lation " does not exactly correspond with the exudate 

 observed by us : the former is found to occur when ticks 

 are numerous, whereas the latter is most marked on cattle 

 on which few or no ticks are present.* With regard to the 

 suggestion that it is a discharge from the ticks, it has been 

 noticed that certain ticks of the genus Ornithodorus when 

 feeding " become surrounded by a clear fluid which comes 

 from their malpighian tubes and coxal glands. "f 



Although we have failed to find even larval ticks in the 

 great majority of the patches of exudate examined by us — 

 even after using the microscope, we believe they are a 

 direct result of larval tick attack on certain cattle, i.e., 

 cattle which possess some individual physiological peculi- 

 arity. Such animals are resistant and apparently the small 

 quantity of tick toxin — perhaps even the mere mechanical 

 stimulus of the rostrum — is able to so increase the local 

 blood pressure that there is an exudation of lymph. We 

 have already stated our opinion that the blood of resistant 

 animals will be found to possess certain differences in regard 

 to its biochemical composition. 



It may be objected that this exudate makes its first 

 appearance each season before the presence of ticks is noticed, 

 but we must point out that larvse begin to infest cattle some 

 little time before their occurrence is noted by an ordinary 

 observer. 



Summary. 



The cattle tick in Queensland may cause tick fever 

 and tick worry. 



There exists a degree of resistance to tick fever and this 

 is largely influenced by individual idiosyncrasy, age, sex, 

 and general health of the animal as well as by food and other 

 conditions. 



Tick worry is at present a more serious complaint than 

 tick fever in Queensland. It is apparently due, at least in 

 part, to the injection of a toxin by the tick. 



*See also Herms. Jour. Parasitol. 2. 1916, p. 140. 

 fPatton and Cragg, Medical Entomology, 1913. p. 639 



