Theobald Smith in 1890 described certain differences in the virulency, morphology and cultural growth between the tubercle bacilli found in human tuberculosis and in bovine tuberculosis. Koch at once commenced a series of experiments, with the result that he not only confirmed the observations of Smith but went further and announced at the British Congress for Tuberculosis in 1901 the following conclusions:
1. The tubercle bacilli of bovine tuberculosis are different from those of human tuberculosis.
2. Human beings may be infected by bovine tubercle bacilli, but serious diseases from this cause occur very rarely.
3. Preventive measures against tuberculosis should therefore be directed primarily against the propagation of human tubercle bacilli.
Koch has been persistently misquoted and the impression is deeply implanted in the lay and medical mind that he denied absolutely the possibility of human infection from the bovine type of the tubercle bacillus. In order to offset