Theobald Smith. Portrait of Theobald Smith (1859- 1934), American bacteriologist who worked on Texas cattle fever and tuberculosis. Smith worked on the nature and control of animal diseases. In 1889 he discovered the protozoan Babesia bigemina which caused Texas cattle fever and in 1893 the tick Boophilus bovis that transmitted it. He published his results in Nature, Causation and Prevention of Southern Cattle Disease. This work paved the way for the acceptance that mosquitos transmitted malaria and yellow fever. In 1896 he distinguished the difference between the bacilli responsible for the human and cattle forms of tuberculosis.