TEXAS FEVER. 481 



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 laying of the eggs to their hatching varies consid- 

 erably, according to the temperature. In the laboratory in the heat 

 of midsummer this was accomplished in about 13 days. In the late 

 fall, under the same conditions, it required from four to six weelis. 

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

 and is just visible to the naked eye. (PI. XL VI, fig. 3.) If these 

 larvae are kept on a layer of moist sand or earth in a covered dish, 

 they may remain alive for months, but there is no appreciable in- 

 crease in size. So soon, however, as they are placed upon cattle 

 growth begins. 



On pastures these little creatures soon find their way on to cattle. 

 They attach themselves by preference to the tender skin on the 

 escutcheon, the inside of the thighs, and on the base of the udder. 

 Yet when they are very numerous they may be found in small num- 

 bers on various parts of the body, such as the neck, the chest, and 

 the ears. (PI. XL VIII and PL XLIX, fig. 1.) 



The changes which they undergo during their parasitic existence 

 were first studied by Dr. Cooper Curtice, of the Bureau of Animal 

 Industry, in 1889. The young tick molts within a week, and the sec- 

 ond 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 adiilt, stage. Impregnation noAv takes place, and, with the 

 development of the ova in the body, the tick takes an increased quan- 

 tity of blood, so that in a few days it becomes veiy much larger. 

 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 

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

 ground in the summer season, they can not mature except as para- 

 sites on cattle and horses. We have purposely omitted various details 

 of the life history, including that of the male, as they are not neces- 

 sary to an understanding of our present subject — Texas fever. How 

 this is transmitted we will proceed to consider. Before the enforce- 

 ment of the Federal quarantine southern cattle sent north during the 

 spring and summer months carried on their bodies large numbers of 

 the cattle ticks, which, when matured, would drop off and lay their 



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