INFECTIOUS DISEASES OF CATTLE. 607 



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 where the cattle emerge 

 after passing through the vat. A drip chute, or floor, is connected 

 with the exit where 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 Farmers' Bulletin 378 and Bureau 

 of Animal Industry Circulars 174 and 183, which may be obtained 

 from this department. It is relatively more expensive to dip cattle 

 in the South, where the farms and plantations contain a small num- 

 ber of cattle, than in the range country of the Southwest, where this 

 method of eradicating ticks becomes not only plausible and prac- 

 ticable, but also economical. 



IMMUNIZATION OF SUSCEPTIBLE CATTLE. 



By hlood inoculation. — 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. Previous to the discovery of the 

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

 duce 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 causing 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. Young animals 6 to 

 15 months old should, so far as possible, Idc selected for this purpose, 

 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. 



Immunity in these cattle is obtained by introducing the micro- 

 parasite of the blood into their systems. It may be done by direct 

 artificial inoculation or by placing virulent young ticks upon the 

 animals and allowing them to perform the inoculation in the natural 

 manner. The subcutaneous injection of a small amount of defibri- 

 nated virulent blood has been found, by means of prolonged experi- 

 ment, the preferable method, as the number of microorganisms intro- 

 duced can be more accurately gauged from the syringe than by 

 allowing the infection to be produced by bites of ticks. Two or three 

 inoculations, if repeated at proper intervals, are accomplished with 

 greater safety to the animal than would be possible by means of a 

 single inoculation. The amount first injected should be small and 

 then gradually increased in the succeeding treatments. 



