The Correlation between the infecting Doses of Tubercle Bacilli and the Survival Curve of Mice in Experimental Tuberculosis

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Host-parasite system is a important factor for the studies on the virulence or immunity in the experimental tuberculosis. Data will be present ed in this paper at first bearing about the selec tion of strain of mice and mycobacteria for ex perimental condition, when the response of mice will be measured by survival test. Strains of mice used as host were CF1 and ddK line, and tubercle bacilli used as parasite were H37Rv of human type, Miwa and Ravenel strains of bovine type. 1) Pathogenicity of tubercle bacilli for CF1 mice. 0.5mg wet weight of H37Rv, Miwa and Ra-venel strains were suspended in 0.2ml of 0.9 per cent saline, and injected intravenously into the tail vein of mice. Then, the survival times of each group of mice were recorded. All mice challenged with Ravenel strain have died within 30 days after challenge infection, and many remarkable tubercles in lungs and enlarged spleens were seen in all mice. On the other hand, mice challenged with H37Rv or Miwa strain were all survived over 30 days, and scarcely remarkable tubercle formation were seen in lungs. From these results it has been conceivable that Ravenel strain is the most virulent against CF1 mice. 2) Susceptibility of mice for tubercle bacilli, Ravenel strain. Fifteen mice of each group, CF1 and ddK strain, were challenged intravenously with 0.5mg wet weight of Ravenel strain, and their survival days were recorded. As shown in figure 1, CF1 mice were more susceptible for tubercle bacilli than ddK mice. Moreover, CF1 mice are believed to be more pure line in hereditary from the comparison of the survival (.curve of each experimental group of mice. 3) The response of mice to BCG vaccination. Figure 2 shows the difference between the response of two strains of mice to vaccination. The effect of vaccination on the resistance pro duced in mice to challenge infection can be measured by comparing the median survival times of vaccinated and nonvaccinated animals. In the group of CF1 mice, the median survival time of vaccinated mice has been prolonged 14.3 days over than that of control, on the other hand, this prolongation has been only 4.0 days in the group of ddK mice. 4) The correlation between the size of infect ing doses and the survival time of mice. 0.5, 0.3, 0.05 and 0.02mg wet weight of Ravenel strain were injected in each 15 mice and recorded the survival time. As shown in figure 3, the median survival time of mice was in inverse ration to the logarithm of infecting dose. This result is agree with the data from Youmans et al. and suggest that the death of mice is presumably dependent upon the viable bacillary level in the host. However, the distribution of deaths did not show always the normal frequency pattern, namely, the lesser was the size of infecting dose, the more was the number of mice died later. If the consideration was given to the result from the survival curve shown in figure 4, the curve of mice infected a large dose was one phase line, and yet the curve of mice in fected a small dose was two phases line. The curve of BCG vaccinated mice in figure 2 was in pallalel with the second phase in figure 4. Therefore, it may be seen that the appear ance of the second phase in the survival curve is based on the acquirement of immunity in the host.
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The Correlation between the infecting Doses of Tubercle Bacilli and the Survival Curve of Mice in Experimental Tuberculosis

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