434 DISEASES OF CATTLE. 



its host. It is unable to come to maturity and reproduce its kind 

 unless it becomes attached to the skin of cattle, whence it may obtain 

 its food. 



The eggs laid on the ground after the female has dropped from the 

 host begin to develop at once. When the embryo is fully formed within 

 the shell it ruptures this and gains its freedom. The time required 

 from the laving of the eggs to their hatching varies considerably 

 according to the temperature. In the laboratory in the heat of mid- 

 summer this was accomplished in about thirteen days. In the late fall 

 under the same conditions, it required from four to six weeks. The 

 larva after emerging from the egg is very minute, six-legged, and just 

 visible to the naked eye. (Plate XLIV, Fig. 3.) If these larvae be kept on 

 a layer of moist sand or earth in a covered dish they may remain alive 

 for mouths, but there is no appreciable increase in size. As soon, how- 

 ever, as they are placed upon cattle growth begins. 



On pastures these little creatures soon iind their way upon cattle. 

 They attach themselves by preference to the tender skin on the escutch- 

 eon, the inside of the thighs, and on the base of the udder. Yet when 

 they are very numerous they may be found, in small numbers, on vari- 

 ous parts of the body, such as the neck, the chest, and the ears. 



The changes which they undergo during their parasitic existence 

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

 within a week molts and the second or nymphal stage of the parasite's 

 life is thus ushered in. After this change it 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. Impregnation now 

 takes place, and with the development of the ova in the body the ani- 

 mal 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 it drops to the ground 

 and begins to lay a large number of eggs, which hatch in the time given 

 aboA 7 e. 



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

 the young or larva? may live for a long time on the ground in the sum- 

 mer season they can not mature excepting as parasites on cattle. 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 pres- 

 ent 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 themselves to the 



