Comparisons of growth curves and generation times of four strains of M, lepraemurium, Kurume No. 42, Hawaii, Kumamoto and Fukuoka No. 1, inoculated into the foot-pads of the dd and C₃H strains of mice were made, and the results obtained were as follows; one step growth curve was observed in the foot-pad of the dd mouse in the case of all strains of M. lepraemurium tested. On the other hand, in the case of the C₃H mouse, one step growth curve of Kumamoto and Hawaiian strains, and the two-step growth curve of Kurume No. 42 and Fukuoka No. 1 strains were observed.
The Kurume No. 42 and Fukuoka No. 1 strains had approximately 4 days' generation time. The Hawaiian strain and Kumamoto strain had 6-8 days and 4 days, respectively, when the bacilli were inoculated into the foot-pad of the dd mouse. When the bacilli of Hawaiian strain and Kumamoto strain were inoculated into the C₃H mouse foot-pad, the generation time of the former was approximately 4 days and that of the latter was 10 days. In conclusion, there might be two types of M. lepraemurium; the one would be the M. lepraemurium whose growth should be modified by the strain of mice employed, and the other would have a characteristic growth rate which should not be influenced by the type of mice used.

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The thyroid tissue becomes destroyed in the mice previously injected with sodium iodine (¹³¹I), this destruction causes the body temperature to fall. Leprous bacilli were injected into the above treated mice and then the multiplication process of the bacilli were examined.
The mice were injected subcutaneously in the back with sodium iodine, 50μc per each animal. Approximately a month later human leprous material was injected. At this juncture the average body temperature of the mice was caused to fall about 1°C in contrast with the average body temperature of the control animals. It is generally recognized that the lowering of body temperature is related to the destruction of thyroid tissue. Into the testes of these mice human leprous material designated LL 11, 21, 22, 23 were injected. This leprous material was emulsified and diluted. The number of bacilli injected were from 15, 000 to 40, 000 per one mouse. In this dilution, of course, small bacterial groups were found. The harvests of acid-fast bacilli in these testes were examined microscopically in every 16 months after the injection.
Retults: Up to 6 and 8 months after the injection of the leprous material into the testes of mice injected with sodium iodine, and the control animals (that is having no sodium iodine), acid-fast bacilli were found both scattered or gathered extracellularly (+s); small groups of bacilli were sometimes found. Up to 10 and 16 months after injection into treated mice, the cells with acid-fast bacilli were found to be abundant, thus forming the socalled globi (+G), which were found often in the capsel of the testis by the histological examination. The round form of globi were not found in this experiment, but the spindle forms of globi were observed. The acid-fast bacilli in the globi changed into segmented forms 16 months later.
From these results, tite can be inferred that the natural resistance of mice injected with sodium iodine is less than in the control mice. It was considered that resistance of the reticuloendothelial system (RES) had been diminished by the sodium iodine injection.

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Experiments to bring about a diminution in the natural resistance of animal have already been made by workers.
The effect of sodium iodine on the innate immunity of mice was studied by the clearance of blood by the reticulo-endotherial system (RES). Mice were injected with sodium iodine (injection dose was 50μc per animal). After the injection, three intervals of time were setup. These were (a) a three-day interval after injection, (b) a 2-week interval after injection, and (c) a 5-week interval after injection. Nine mice were used respectively for each of above 3-time intervals, so 27 animals in all.
Next, all 9 mice of the 3-day interval were injected intravenously with 1mg of E. coli suspended in 0.1ml of NaCl solution. The E, coli had been cultivated for 24 hours in a incubator. Then 3 mice were selected from the nine, immediately after the injection of E, coli and the blood was taken from the heart by means of a syringe containing sodium citrate.A group of 3 other mice were similarly treated at a 30-minute interval after the injection of E. coli, and the remaining 3 mice at a 60-minute interval after the injection.
The amount of blood sample taken by the syrings was 0.5ml. Next, the liver, spleen and testes of each mouse were taken and emulsified. The concentration of these emulsions was adjusted to 100mg/ml, and the same organ emulsions of the 3 mice in each group were pooled respectively. Then, smples of the blood and of the liver, spleen and testes were diluted with NaCI solution, poured into Petri-dishes together with melted agar and cultivated for 48 hours in an incubator.
The bacterial colonies on the plates were counted, and the average number of bacteria in 1ml of blood was compared with that in the control animal. The similar procedures were repeated on the 9 mice in the 2 week and 5 week intervals. The results indicated that in the 9 mice injected with 50μc of sodium iodine and injected itravenously 3 days later with E. coli, the bacilli in the 30-minute animal were diminished and much more in the case of 60-minute animal. The clearance ability of sodium iodine injected mice was about the same as in the control mice. In those 9 mice which were injected with sodium iodine and injected intravenously 2 weeks later with E. coli, the 30 minute animals showed a decrease of bacilli in the blood stream and the 60-minute aniamis showed slightly more diminution. The untreated control mice showed a greater diminution of the bacilli (E. Coli) than the treated mice. When the mice were injected with E. coli 5 weeks after the sodium iodine injection, the "30-minute" and "60-minute" animals showed abundant numbers of bacilli in the blood stream in contrast to the diminution of the clearance ability in the control mice. Human leprous material was injected into the testes of these animals. The average body temperature during this week indicated a fall of about 1°C. The clearance ability of the liver, spleen and testes of the mice as tested, but it was not so significant as shown by figures of the blood stream.

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We reported the previous communication as "an attempt to cultivate the murine leprosy bacillus". In this communication, something was unsatisfactory. For the purpose of supplementing it, here we are going to state on the results obtained during the period from September, 1969 to May, 1970.
1) Isolated culture and subculture: The method is almost same in the report 1. As for the result of isolated culture, out of 10 specimens, none of the specimens from mice of 1-4 months' duration proved positive. In materials from mice of 5-11 months' duration, 6 specimens (15%) of 40 specimens in non-treated ones, 23 specimens (25%) of 92 specimens in the group treated by 1% NaOH solution and 3 specimens (25%) of 12 specimens in the group treated by 1% sulfuric acid solution proved positive. When the result is classified by number of bacilli contained in inoculated specimens, as the number of bacilli increased, the positive rate became better. As for the subculture, at present 8th generation are going.
2) Reproduction test: The test was made with primary culture and the third subculture of Hawaiian strain-like acid-fast bacilli. 0.2mg in case of subcutaneous infection and 0.1mg in intravenous infection of the both were inoculated to mice of dd-N strain, and the infected mice were killed at various intervals, autopsied, and examined according to the method previously reported. The result revealed that both strains of the primary culture and the third subculture porduced lesions which were evident macroscopically and histopathologically. In case of subcutaneous infection, the lesions were almost slight, but in the case of intravenous infection they were generally highly advanced. The local lesion was evident at the site of inoculation in the case of subcutaneous infection. These lesions advanced in the course of infection. Also positive cultures were obtained from the spleen and the local lesion of subcutaneously infected mice and from the spleen, liver and lungs of mice of long duration after the intravenous infection. Morphological and cultural characteristics of the organisms thus obtained were much the same as that of the original culture employed for infection.

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