Protozoan Cattle Fever. Texas Fever. Paludism of Cattle. 613 



should be placed on the skin so that the system may be thoroughly 

 habituated to them and the measure of resistance correspondingly 

 strengthened. 



This measure may be advantageously applied to valuable cattle 

 that are to be. moved into the infecting territory, but it has 

 serious drawbacks. The relative strength of the poison intro- 

 duced by the ticks to the susceptibility of the animals on which 

 they are placed, can never be perfectly gauged, and a certain 

 small but appreciable number of deaths result from this first in- 

 festing. This has been observed in North and South America, 

 Australia, Roumania and Turkey. Again, the plan entails the 

 necessity for clean, noninfected premises (lots or buildings) for 

 each fresh lot of cattle, as the places previously used are left in a 

 tick-infested condition, and are likely to furnish a dangerous ex- 

 cess of ticks to any susceptible animal. The buildings could, of 

 course, be disinfected and purified, but this entails considerable 

 expense. 



c. Infection by Graduated Injections of Blood Containing the 

 Pyroplasma. Up to the present this is the most promising 

 method of securing resistance to the pyroplasma. It is advised 

 to take the blood from an immunized northern animal or from 

 one indigenous to the infected district. Such an animalis not, 

 however, strictly speaking immunized. It has acquired a toler- 

 unce so that it is no longer in much danger of succumbing to the 

 pyroplasma, but it does not exclude the pyroplasma from its sys- 

 tem. The micro-parasite is still found in the blood, though 

 mainly in the coccus- like form in the interior of the red globules. 

 The animal to be fortified against the disease is therefore inocu- 

 lated with the germ of the disease itself, though it may be, at the 

 time, in a somewhat inactive form. If, however, the inoculated 

 animal is specially susceptible, or if the dose is excessive, the dis- 

 ease is produced in deadly form. The virulence is less in the 

 case of blood drawn from a northern animal just recovered from 

 the disease, than from an animal indigenous to the infected dis- 

 Irict, and which harbors the pyroplasma, it may be in spore form 

 (I/ignieres) , without showing obvious disease. The former 

 source of the blood is therefore the more desirable, while the 

 latter is the more easily obtained. The precaution, however, 

 should be adopted of reducing the dose when taken from an in- 



