498 DISEASES OF CATTLE. 



mals before they are dry should also be prevented, and they should 

 not be driven any considerable distance within a week after dipping, 

 especially in hot weather. If many repeated treatments are given, 

 the cattle should not be treated of tener than every two weeks. 



In addition to properly protecting vats containing arsenical dip 

 when not in use, caution must also be observed when vats are to be 

 emptied for cleaning. The dip should not be poured or allowed to 

 flow on land and vegetation to which cattle or other animals have 

 access. The best plan is to run the dip into a pit properly protected 

 by fences. The dip should also not be deposited where it may be 

 carried by seepage into wells or springs which supply water used on 

 the farm. 



Crude petroleuTn. — Various kinds of crude petroleum and emulsions 

 of it have been used with more or less success in destroying ticks, but 

 on account of the difficulty of obtaining suitable grades of oil and the 

 liability of injury to cattle, their use has been practically abandoned. 



Method of dipping. — The method usually adopted in dipping cattle 

 is to construct a narrow swimming tank with a chute at one end for 

 the entrance of the cattle, and a sloping exit at the other end when 

 the cattle emerge after passing through the vat. (SeePl. XLIX,fig. 

 2. ) A drip chute, or floor, is connected with the exit, Avhere the excess 

 of dip is allowed to drip off the animals and to drain into the vat. 

 Plans and specifications for installing dipping plants are published 

 in Bureau of Animal Industry Circular 207, which may be obtained 

 from this department. 



IMMUNIZATION OF SUSCEPTIBLE CATTLE. 



By hlood inocyZation. — It is often desirable to ship well-bred cattle 

 into infested districts that they may be used to improve the quality 

 of the native cattle already there. Prior to the discovery of the cause 

 of Texas fever it was found to be well-nigh impossible to introduce 

 purebred cattle from the North into any of the infected regions 

 without suffering great loss — sometimes as high as 90 per cent — 

 within a few months of their arrival at their southern destination. 

 At first it was thought that the fatalities were due to climatic 

 changes, but later the discovery was made that Texas fever was caus- 

 ing these numerous deaths. 



It has now been found practicable to immunize this class of cattle 

 so perfectly that the losses which follow their transportation to a 

 tick-infested region are reduced to a minimum. So far as possible, 

 young animals 6 to 15 months old should be selected for this pur- 

 pose, as they are more readily immunized than adults, are more easily 

 handled, and the dangers which may arise from pregnancy while 

 undergoing the immunizing treatment are thus avoided. 



