222 A TK'K-RESISTANT CONDITION IN CATTLE. 



blood containing the piroplasm*. Animals which have passed 

 through one attack of tick fever may pass throixgh a second 

 or even a third attack, especially if the vitality of the 

 cattle becomes lowered by adverse conditions, e.g., if they 

 be over-driven, ronghlj' handled, more or less deprived of 

 food and water, etc. Dodd (1908, p. 16) states that the 

 poAver of the micro-parasite varies a great deal in different 

 regions and the immunity which maj"- be sufficient in one 

 district may not be enough to protect the cattle if moved 

 to another district. He goes on to ^say that it is a well- 

 known fact both in Queensland and Soiitli Africa that cattle 

 which are immune in one district have contracted tick fever 

 again when removed to another. Cory (1916, p. 80) stated 

 that it had been frequently noticed that toleration broke 

 doAvn when cattle were removed to another tick infested 

 district although they were apparently immune against 

 pathogenic ticks before rem oval f. 



Protective inoculation is widely practised in Queensland,, 

 especially in the case of stock imported from tick-free 

 districts into ticky country. This operation does not 

 really " protect " the animal from piroplasmosis but actually 

 causes an attack of the disease which, however, is generally 

 less severe and usually minimises the danger from a subse- 

 quent attack. Such, however, may occur but they are as 

 a rule quite mild. In Queensland, blood for inoculation 

 is nearly always taken from a " recovered animal," that is, 

 one which has apparently recovered from tick fever. Such 

 " recovered blood " is injected with due precaution into 

 the cattle which it is desired to protect. The method 

 locally practised has been carefully described by various 

 workers (Hunt, Pound, Dodd, Tidswell and others). The 

 mortality from natural tick infection in the case of 



*Hunt and Collins (1896, p. 6-7) refer to a case in Washington, D.C.,. 

 U.S.A., where l^lood taken from a cow which had bean kept away from 

 ticks and tick-infested districts for over six years, set up virulent (and 

 sometimes fatal) tick fever on inoculation into susceptible cattle ; and 

 yet after careful examination of four thousand blood smears, only fir* 

 infected corpuscles were found by Schroeder and Kilbome. 



fA number nf Queensland instances are quoted by the Editor, 

 Queensland Agr. Journai, 20, 1908, pp. 325-7, in an article entitled 

 " Tick fever — Is general immunity attaina)>le ? " 



