BY T. HARVEY JOHNSTON AND M. J. BANCROFT. 291 



" Winter Ticks." 



Mr. Hull repeatedly claims that his resistant animals 

 mature more ticks in winter than in summer. We think 

 that this is probably due to the fact that the cows which 

 are under closest observation, are the milkers. During 

 the winter, milking cows frequently fall into somewhat 

 low condition, which, as is well known, brings about a 

 diminution of their tick-resisting properties. Resistant 

 cows when dry, seldom become tick infested. 



We might mention that occasionally during both 

 summer and winter, we received specimens of Rhipice- 

 phalus sanguineus taken from cattle and from a horse 

 (Eumundi), while Mr. Inigo Jones forwarded during last 

 winter a number of ticks ( Hcema'physalis sp.) which he had 

 collected from his cows (Crohamhurst). 



Is Resistance Transmissible ? 



Mr. Hull claimed that the peculiarity is transmissible,. 

 (1) hereditarily ; (2) bj^ vaccination ; (3) by contact. 



Mr. Pound (1014, p. 110) published a statement pre- 

 pared by Mr. Hull, giving a list of his resistant cattle (31st 

 March, 1913) under the headings, {a) resistant by vaccin- 

 ation, 6 ; (h) by contact, 7 ; (c) by heredity, 6 ; while the rest 

 of the herd (38) were at the time all more or less infested. 



1. Transmission by Heredity : — Mr. Hull maintains 

 that the progeny of resistant animals become resistant, 

 though such quality does not usually manifest itself until 

 after the first year of life. The occurrence of some cases 

 of animals showing a strong resistance to tick infestation 

 from birth seems to support the hypothesis. 



Mr. Pound has reported adversely, mentioning that 

 Clover's calf and Tinkerbell's calf were just as liable to tick 

 infestation as an ordinar}' animal (1914, p. Ill, 112, ; 1916, 

 p. 90 ; R.S.C., p. 21 ; Corser, R.S.C., p. 64 ; Thorn, R.S.C., 

 p. 28). Clover's calf was two and a half years old and the 

 other six months, in October, 1915. In March, 1915, one 

 of us visited Yeerongpilly and was shown a young calf 

 from Tinkerbell as well as Clover's heifer, both of them 

 markedl}^ infested with fully engorged ticks as well as others 

 in earlier stages. Information was given by Messrs. Pound 

 and Thorn that these ticks were applied as larvae in February. 

 Infestation in this case was artificial as it was in 1917 



