INSECTS INJURIOUS 'J(» CATTLE 417 



tion to it. These may be divided into three classes : 

 Protective influences within tire infested area, outside 

 of the same, and for cattle brought into the infested 

 area. 



It should be quite possible to exterminate Texas 

 fever on any farm, although this is not always easily 

 done. The fact that the fever cannot be imparted ex- 

 cept through the medium of the ticks, and that the ticks 

 cannot survive apart from the bodies of cattle for a 

 longer period than, say, four to five months, is of 

 great significance. It means that the pasture infested 

 may be freed from the presence of ticks in one season 

 if cattle are kept aloof from them from September on- 

 ward. If cattle without ticks are then introduced and 

 confined within a properly fenced yard, the work is 

 done. The introduction of such cattle, even from in- 

 fested areas, has been made quite possible through sub- 

 jecting them to dipping in or spraying with the crude 

 petroleum preparation, according to the regulations 

 prescribed by the United States Department of Agricul- 

 ture. 



Outside the infected district infection cannot follow 

 unless cattle are brought from the infected district within 

 the months during which such removal is not permissible 

 or unless they are exposed to infection from quarters 

 occupied by infected cattle when being sent northward 

 for slaughter. The dipping process referred to above 

 makes it possible to ship in cattle from infected areas. 

 This, however, is but little desired except when the cat- 

 tle are brought in for grazing or finishing for the block. 



It is frequently desirable to bring cattle within the 

 infected area for breeding uses chiefly with a view to 

 effect improvement in the cattle ordinarily kept within 

 the same. Happily this is now quite possible by ren- 

 dering them immune to the disease by means of inocula- 

 tion. This is usually done in the following way: Some 

 of the blood of an animal over two years of age that was 



