TEXAS FEVER. 499 



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 

 nnimals and allowing them to perform the inoculation in the natural 

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

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

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

 troduced can be more accurately gaged from the syringe than by 

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

 inoculations, if repeated after proper intervals, are accomplished 

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

 a single inoculation. The quantity 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 

 termination ; but the proportion of deaths resulting from the inocu- 

 lation is small when compared with the fatalities among untreated 

 animals taken into infested districts. To this number should be 

 added those animals (less than 7 per cent) that do not receive sufficient 

 immunity by this method and which succumb when exposed to in- 

 fested pastures. Combining these failures it will be seen that by this 

 method of immunization, instead of a loss of 90 per cent among 

 breeding stock taken South more than 90 per cent can be saved. The 

 animals should be carefully nursed through the attack and their 

 symptoms treated as indicated on page 502, 



Immunizing inoculations are now being made by the veterinarians 

 of most of the agricultural experiment stations of the Southern 

 States without cost for the services rendered, a charge being made 

 merely for the actual value of food consumed and attendants' wages. 

 These veterinarians have also issued station bulletins which describe 

 fully the necessary steps to be taken in obtaining the blood and in- 

 jecting it into the animals to be immunized, so that the stock owner 

 may follow the instructions with prospects of getting good results. 



This operation is not a difficult one, and excellent results will fol- 

 low when absolute cleanliness and ordinary care have been used, but 

 undoubtedly the best results will be obtained by those who have 

 thoroughly familiarized themselves with the nature of the disease 

 and are experienced in extracting blood from animals. Two methods 

 are in use and will be described separately. One consists in drawing 

 the blood from the jugular vein of an immune animal and immedi- 

 ately injecting it into the cattle to be immunized. It is compara- 

 tively simple, requires few instruments, and can be satisfactorily 

 carried out when a small number of animals are to be immunized 

 and if a suitable immune animal is close at hand. First, select an 



