Protozoan Cattle Fever. Texas Fever. Paludism of Cattle. 557 



into their victim. Cattle taken from the northern states and 

 placed on southern pastures, or passing over trails already well 

 stocked with the ticks, are infected at once and sicken in from 

 three to ten days. Cattle in their northern home placed on a 

 previously uninfested field with southern cattle just arrived, do 

 not suffer for thirty, forty, sixty, and in exceptional cases, even 

 ninety days. The paradox is explained by the time wanted for 

 the laying of the eggs and the hatching of the tick larvae. The 

 female tick does not lay eggs until she is fully mature, and if the 

 ticks on a southern ox are .still immature there is a variable 

 period of delay until the eggs are mature enough to be deposited. 

 Then the ovigerous tick drops off her host and spends one week 

 in laying her eggs. In warm weather these eggs take three to 

 four weeks to hatch, so that u,sually five weeks elapse before the 

 young (seed ticks) can climb upon the ox and infect him. Add 

 three to six days more for the actual incubation and we ac- 

 count for about six weeks of delay in the appearance of the 

 disease in northern cattle. If we consider further that a wet .sea- 

 son occurring after the eggs have been laid and before they are 

 hatched tends to divest them of their protective covering and to 

 expose them to destruction, and that, in any case, a cold season 

 will delay the hatching until the recurrence of warm weather, 

 and that the absence of bovine victims will doom the new-born 

 larva to an arrest of development, so that a further indefinite de- 

 lay may be entailed, we have abundant explanation of the fre- 

 quently delayed evolution of symptoms. Yet in general terms 

 the apparent prolongation of incubation is due to fortuitous cir- 

 cumstatjces which delay the infection, and not to any actual ex- 

 tension of the incubation itself. 



Symptoms of Acute Type. Cattle infected outside the area of 

 habitual prevalence and stock from non-infected districts, con- 

 veyed into the infected ones in hot weather, u,sually contract the 

 disease in its acute and fatal form. The period of the year is 

 often significant, a number of animals being attacked at once in 

 the hot dry period of late summer or autumn — July to September 

 in North America, February to May in Argentina. 



The first symptom is a rise of temperature, and this may la.st 

 two or even three days before other morbid phenomena are 

 noticed. It may rise to 104° F. in the first day and later to 107", 



