When the disease is prevalent or scattered beyond the infected district the roads, barns and pastures are dangerous until freezing weather, when the disease disappears and cattle can be kept in the grounds or driven over the roads without catching the disease. The midwinter months is the only time that cattle can be safely driven from an infected area to a non-infected area without spreading the disease. =The Cause.=--Texas fever is caused by an organism which lives within the red-blood corpuscles and breaks them up. It is not a bacteria, but a protozoa, and belongs to the lowest forms of the animal kingdom. How it gets into the blood corpuscles is not known. The fatality is due not so much to the loss of blood corpuscles as to the difficulty which the organs have in getting rid of the waste products arising from this wholesale destruction. =The Course of the Disease.=--After a period of exposure, which may vary from 13 to 90 days, the disease first shows itself in dullness, loss of appetite and a tendency to leave the herd and lie down alone. A few days before these symptoms appear the temperature rises from 103° to 107°. There is little change in temperature until death or recovery. =Pathological Changes Observable After Death.=--The presence of small ticks on the udder or escutcheon is a very important sign in herds north of the Texas fever line. The watery condition of the blood. The spleen or milt very much enlarged, and filled with a blackish pulp. Enlargement of the liver, and its color changed to a mahogany color. The distended gall-bladder, caused by an excessive amount of bile in it. =The Cattle Tick= (_Boophilus bovis_) is the carrier of this disease. Its life history is quite simple. 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 by the female tick after falling off the cattle begin to develop at once. The time required for hatching varies considerably, according to the temperature. In the heat of summer about 13 days, and in the fall, under the same conditions, from four to six weeks. 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. When very numerous they may be found on various parts of the body. They remain clinging to the cattle until mature, and then fall off and lay their eggs and hatch more new ticks.