306 A TICK-RESISTANT CONDITION IN CATTLE. 



albipictus to cattle, but only a few engorged females were 

 developed from them. 



Fairly frequently one may meet with undersized 

 yellowish female ticks in which the malpighian tubes 

 appear to occupy a great deal more than the normal space. 

 Such ticks apparently are nearly always unable to engorge. 

 They occasionally lay a comparatively few pale eggs which 

 in every case failed to hatch, although from eggs from 

 three specimen.s of such ticks (December, 1915), larvae were 

 developed but failed to emerge. It may be objected that 

 such ticks have not been fertilised but those which have been 

 dissected have contained abundant spermatozoa. Such 

 ticks have been taken from a number *of resistant animals 

 and also from certain cows which are at present classed as 

 non-resista,nt. At least one of the latter, viz. Vixen, is 

 regarded as " cleaning up " as far as tick infestation is 

 concerned. Mr. Henderson (R.S.C., p. 41) referred to this 

 type of tick as occurring on his " immune " stock. 



In this coniiection we might draw attention to the 

 following observation by Dr. Wynne (1896, p. 40) : 

 " Ascites of female tick. One morbid condition of the 

 adult female tick is worth noting though I am unable to 

 offer any explanation. Very rarely and apparently only 

 on certain animals the ticks look like miniature white 

 grapes, almost transparent, of a pale greenish yellow. 

 They are little bags of fluid, in the interior of which the 

 various internal organs can be seen lying. It appears to 

 be a true dropsy of the peritoneal cavity as on dissecting 

 the tick the condition of the organs recalls vividly the 

 appearances seen in ascites of man." 



The ticks referred to by us are certainly not like " bags 

 of fluid " but are somewhat shrunken. 



Exudate. 

 Associated with tick resistance may be an exudate. 

 This exudate, or so-called serum, has on many occasions 

 been referred to by Mr. Munro Hull, who was, as far as we 

 know, the first to bring it under public notice in Australia. 

 It consists of drops of a clear yellow fluid, which appear on 

 the skin on various parts of the body, neck, dewlap, butt 

 of tail and escutcheon, notably on the last-named, where 



