When leprosy bacilli from human patients are inoculated into the foot-pads of CFW mice, a microscopic granuloma containing acid-fast bacilli develops in a characteristic manner. This has been seen in 22 of 22 instances with leprosy bacilli from nasal washings, in 12 of 16 instances with leprosy bacilli from skin biopsies, and in none of 16 cases where the nasal washings were not observed to contain leprosy bacilli.

Quantitative studies revealed a relationship between the number of bacilli inoculated and the time required for the appearance of the lesions. The incubation period was usually 1 to 2 months when the dose was 105.5 to 106.0 bacilli and about 6 months when the dose was about 103 organisms.

After the development of the lesion, the number of bacilli harvested was usually in the range 104.5 to 106.0, regardless of the number inoculated. When the inoculum has contained 102.0 to 103.5 acid-fast bacilli, and harvests were reasonably prompt, there were regular increases of 50- to 1000-fold.

Passage to new groups of mice has been successful 11 of 12 times. Most of these were second passages. One strain has been maintained in 3 passages with a total increase in acid-fast bacilli of 4 x 104-fold. Another strain has been through 4 passages with a total increase of about 4 x 106-fold.

Cultures on bacteriological media favorable for the growth of most known mycobacterial species have not shown growth of mycobacteria.

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