436 DISEASES OF CATTLE. 



Texas fever is carried north only by the cattle tick. That there may be 

 other sources of infection can not be denied, but if there be such they 

 come into operation rarely and perhaps in very restricted localities. 

 Hence, to prevent Texas fever north of the permanently infected area 

 is to keep the pastures free from cattle ticks, and to do this no Southern 

 cattle with ticks must be allowed upon them. Ticks may, however, 

 reach pastures in other ways. Cattle cars from the South may leave 

 the sweepings and manure in places where cattle may get access to 

 them. These will contain ticks or eggs which will give rise to a brood 

 of young ticks in due time, ready to inoculate cattle when the opportu- 

 nity presents. 



How to rid pastures of ticks without destroying the vegetation upon 

 it we do not know at present. Every pasture once infected is dangerous 

 during the entire season. Fortunately the winter destroys the tick and 

 afresh importation from the South is necessary to produce the disease 

 again during the following season. This is not strictly true for sheltered 

 places near the Texas-fever line, for they may live through very mild 

 winters in such places and produce disease the following summer. The 

 precise temperature at which the egg or the various stages of the cat- 

 tle tick are destroyed can not be accurately ascertained, because it 

 depends on the amount of protection and shelter which they may obtain. 

 It is therefore impossible to state how late in the winter ticks carried 

 from the South are still likely to perish in the North before the ensuing 

 spring. We know that cold greatly retards the development of ticks 

 in the egg and afterwards, and that any fatal disease in cold weather is 

 not likely to occur, but if the ticks should survive until summer the 

 danger of an outbreak is imminent. This danger diminishes, of course, 

 the farther north we go and the period of time during which ticks may 

 be carried thither with impunity is greater, owing to the longer season 

 of cold. 



Treatment. When the disease has broken out, all animals, the sick 

 as well as the healthy, should at once be removed to another non- 

 infected pasture. While this may not cut short the disease, it may 

 save the lives of some by removing them from the possibility of being 

 attacked by more young ticks. Removal from infected pastures like- 

 wise prevents a second later attack in October or early in November, 

 which is caused by another generation of ticks. It is true that sick 

 natives infect with a new generation of ticks the pasture to which they 

 are removed, but these usually appear so late that they have but little 

 opportunity to do any damage. Hence, sick natives do not, as a rule, 

 cause visible disease in other natives. 



It is of importance to remove all ticks, as far as this is possible, from 

 sick animals, since they abstract a considerable amount of blood and 

 thereby retard the final recovery. No systematic experiments have as 

 yet been made in the medicinal treatment of the sick, as the study of 

 the cause of the disease has taken all the time that could be given to 



