Theobald Smith (1859-1934), US pathologist. Smith studied animal diseases and methods to control these disease. In 1889 he discovered the protozoan Babesia bigemina which causes Texas cattle fever and in 1893 he discovered that the tick Boophilus bovis transmitted it. He published his results in Nature, Causation and Prevention of Southern Cattle Disease. This work paved the way for the acceptance that mosquitoes transmitted malaria and yellow fever. In 1896 he showed that different bacilli caused the human and cattle forms of tuberculosis. This photograph is from a glass negative, and is part of the George Grantham Bain Collection.