CULTURES of tubercle bacilli from Indian patients have been shown to be, on
average, less virulent in the guinea-pig and to have a wider range of virulence than
cultures obtained from British patients (Frimodt-Moller, Mathew and Barton,
1956 ; Mitchison et al., 1960 ; Bhatia et al., 1961). In the study of Bhatia et al.
(loc. cit.) about one-third of the Indian cultures were as virulent as British cultures,
the remainder being less virulent. In these studies the extent of disease in the
organs of the guinea-pig was scored at intervals after the intramuscular injection of
the organisms. In consequence, the measure of virulence was based upon the rate
of development of the lesions and, by inference, the rate of multiplication of the
bacilli in the organs. It was, therefore, considered of interest to compare the
growth rates in vitro of Indian and British cultures of tubercle bacilli