Smith, Theobald (1859–1934)

US microbiologist and immunologist who demonstrated the involvement of a bacillus (a rod-shaped bacteria) in the onset of tuberculosis (TB), a respiratory disease.

Continuing the previous work of French physician Jean Louis Villemin, Smith made a careful morphological comparison 1896 of tuberculosis bacilli extracted from humans and cows and showed that there were differences. He also demonstrated that they show marked differences in virulence for the ox and rabbit. He proved that there are two distinct types of mammalian tubercle bacillus, one human and the other bovine. It was later proved that the bovine bacillus is transmissible to humans.

Smith also worked on vaccines for smallpox and cholera, as well as diphtheria antitoxins (antibodies). He noted that guinea pigs used for the testing of diphtheria antitoxin became acutely ill if test injections were separated by long intervals. This reaction was later discovered to be caused by hypersensitiveness, or anaphylaxis, by Charles Richet. He also went on to devise ultrasensitive methods for the detection of certain types of bacteria in drinking water, milk, and sewage.

Smith was born in Albany, New York, where he trained as a doctor at Albany Medical College. He went on to become an eminent bacteriologist with research laboratories at Harvard Medical School and the Rockefeller Institute in New York.