336 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



used in cultivating the fields be curried to keep off the ticks and pre- 

 vent the latter from being carried into these fields. Cats should also 

 be kept from the pastures and fields ; for, although they do not har- 

 bor the mature ticks, seed ticks have been found on them, and while 

 these seed ticks remain only for a short period, this time may be 

 sufficient to allow them to be carried into the disinfected pastures, 

 where they may fall off and reinfest the soil. If a farm or planta- 

 tion consists of a pasture and but one field under cultivation, the 

 above plan can be made applicable by fencing off three inclosures in 

 the latter and by rotating the cattle in them every twenty days in 

 the manner just described. The same precautions should be observed 

 in changing the cattle from one lot to another and in preventing 

 ticks from getting into the cultivated field as are mentioned above. 



IMMUNIZATION OF SUSCEPTIBLE CATTLE. 



By Blood 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 introduce pure bred cattle from the North into any of the in- 

 fected regions without suffering great loss sometimes as high as 90 

 per cent within a few months of their arrival at their southern des- 

 tination. At first it was thought that the fatalities were due to cli- 

 matic 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 cat- 

 tle so perfectly that the losses which follow their transportation to a 

 tick-infested region are reduced to a minimum. Young animals six 

 to fifteen months old should, as far as possible, be 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 micro-organisms in- 

 troduced 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. 



The inoculation always results in a more or less serious attack of 

 Texas fever. Besides having a fever, there is great diminution of 

 red blood corpuscles, and in about 3 per cent of the cases a fatal ter- 

 mination; but the proportion of deaths resulting from the inocula- 

 tion is small when compared with the fatalities among untreated ani- 

 mals taken into infested districts. To this number snould be added 



