468 DISEASES OF CATTLE. 



were first studied by Dr. Cooper Curtice in 1889. The young tick 

 within a week molts, and the second or nymphal stage of the para- 

 site's life is thus ushered in. After this change :'t has four pairs of 

 legs. Within another week another molt takes place by- which the 

 tick passes from the nymphal to the sexual, or adult, stage. Impreg- 

 nation now takes place, and, with the development of the ova in the 

 body, the animal takes an increased quantity of blood, so that it 

 becomes very much larger in a few days. That the rapid growth is 

 due to the blood taken in may be easily proved by crushing one. The 

 intestine is distended with a thick, tarry mass composed of partly 

 digested blood. When the female has reached a certain stage of 

 maturity she drops to the ground and begins to lay a large number of 

 eggs, which hatch in the time given above. 



The life of the cattle tick is thus spent largely on cattle, and 

 although the young, or larvae, may live for a long time on the ground 

 in the summer season, they can not mature excepting as parasites on 

 cattle and horses. We have purposely omitted various details of the 

 life history, including that of the male, as they are not necessary to 

 an understanding of our present subject — Texas fever. How this is 

 transmitted we will proceed to consider. 



Southern cattle sent North during the spring and summer months 

 carry on their bodies large numbers of the cattle tick. These when 

 matured drop off and lay their eggs on Northern pastures. These 

 hatch, and the young tick soon gets upon any Northern cattle which 

 happen to be on the pasture. As soon as they have attached them- 

 selves to the skin they inoculate the cattle, and Texas fever breaks 

 out a week or more thereafter. For many years there had been a 

 growing suspicion that the cattle tick was in some way concerned in 

 the spread of Texas fever, and the facts which supported this suppo- 

 sition finally became so numerous and convincing that a series of 

 experiments were inaugurated by the Bureau of Animal Industry 

 which served to show that the tick was abundantly able to carry the 

 disease to a herd of healthy cattle, and in fact was probably the only 

 agent concerned in the transmission of the disease from Southern 

 cattle to susceptible Northern animals. 



The regulations which have been enacted by the Department of 

 Agriculture for the control of cattle shipments from the infected dis- 

 tricts have for their initial purpose the prevention of the transporta- 

 tion of cattle ticks from infected regions to those that are noninfected, 

 either upon cattle or in stock cars or other conveyer, and the exclu- 

 sion of these parasites from noninfected territory has in every instance 

 been found a certain method of excluding Texas fever. 



