CATTLE TICKS AND TEXAS FEVER--The cattle disease, which in the United States is known as Texas fever, is a widely distributed, exceedingly acute disease. In Australia it is known as _redwater fever_ and in Europe as hæmoglobinuria, due to the fact that the urine of the diseased animals is discolored by the breaking down of the red blood corpuscles infested by the parasite. In their historical discussion, Smith and Kilbourne, point out that as far back as 1796 it was noted that Southern cattle, in a state of apparent health, might spread a fatal disease among Northern herds. As observations accumulated, it was learned that this infection was carried only during the warm season of the year and in the depth of winter Southern cattle were harmless. Moreover, Southern cattle after remaining for a short time in the North lost their power to transmit the disease, and the same was true of cattle which had been driven for a considerable distance. Very significant was the fact that the infection was not communicated directly from the Southern to Northern cattle but that the ground over which the former passed was infected by them, and that the infection was transmitted thence to susceptible cattle _after a period of not less than thirty days had elapsed_. Of course a disease as striking as this, and which caused such enormous losses of cattle in the region invaded was fruitful in theories concerning its causation. The most widespread was the belief that pastures were infected by the saliva, urine, or manure of Southern cattle. There were not wanting keen observers who suggested that the disease was caused by ticks, but little weight was given to their view. Various workers had described bacteria which they had isolated from the organs of the diseased animals, but their findings could not be verified. In 1889, Smith and Kilbourne discovered a minute, pear-shaped organism (fig. 138) in the red blood corpuscles of a cow which had succumbed to Texas fever. On account of their shape they were given the generic name _Pyrososma_ and because they were usually found two in a corpuscle, the specific name, _bigeminum_. It is now generally accepted that the parasite is the same which Babes had observed the year before in Roumanian cattle suffering from hæmoglobinuria, and should be known as _Babesia bovis_ (Babes). [Illustration: 138. Babesia bovis in blood corpuscles. After Calli.] [Illustration: 139. The cattle tick (Boophilus annulatus). (_a_) Female; (_b_) male. After Comstock.] By a series of perfectly conclusive experiments carried on near Washington, D.C., Smith and Kilbourne showed that this organism was carried from Southern cattle to non-immune animals by the so-called Southern cattle tick, _Boophilus annulatus_ (= _Margaropus annulatus_) (fig. 139).