In 1965, Hilson claimed the successful transmission of M. leprae into the foot-pad of the white wistar rat. Therefore, we have performed examinations on the multiplication of M. leprae in the hind foot-pads of rats, using materials (M. leprae) of 3 mouse-passages.
Furthermore, we have performed a comparison of the differences in the multiplication rate between rats and mice, and the enhancing effects of cortisone-administration or thymectomy in rats.
White wistar rats were used, and the technics of inoculation and thymectomy were similar to those described by ourselves, as reported elsewhere. The cortisone was intramusculary injected into their hind paws at a daily dosage of 8mg., which administration was continued for 6 days, in the second week after inoculation with M. leprae.
The inoculum was 5.8×10³ bacilli (Fukuzato), 6.4×10³ bacilli (Fujii) and 9.7×10³ (SH-2=N-2401 p₁₂ passage strain isolated by C.C. Shepard) per each foot-pad.
The details are shown in Table 1. In the case of mice, the bacillary counts of M. leprae in each foot-pad rose to a plateau level of at most 10⁶, but in the case of rats it rose to a plateau level of at most 5.0×10⁴-10⁵. The second passage (rat to mouse) examined at 25 weeks after transmission from the first passage in rats showed the bacillary counts of M. leprae similar to that of the first passage in the mice. No growth was observed on Ogawa's medium, and inoculation with M. lepraemurium in the rat foot-pad produced a slighter nodular swelling of the injected foot-pad than that of the mouse footpad. In addition, in the cortisone-administered rat and thymectomized rat the bacillary count did not rise to a plateau level at an early stage after inoculation, the results being different from those of the mouse and hamster, as described elsewhere by ourselves.
In summary, it can be said that we have observed the successful transmission of M. leprae into the hind foo-pad of the wistar rat, but the susceptibility of this animal to M. leprae was less than that of the mouse, as shown by the bacillary count and microcolony of M. leprae in the foot-pad.

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Today, the studies of murine leprosy and the murine leprosy bacillus still maintain an important place as a model in the study of leprosy.
From the finding that when mice are inoculated with the leprosy bacillus, the organism, which proliferates, replaces the murine leprosy bacillus, a study was made of latent murine leprosy bacillus in the mouse and the contamination of various experimental animals by acid-fast organisms, and a new method of investigation utilizing spread smear preparations of subcutaneous connective tissue was devised. The attempt was made to clarify the range of contamination of experimental animals by the murine leprosy bacillus and other acid-fast organisms, and from the results, point out the precautions which must be taken in conducting animal experiments with the leprosy bacillus. The effort was also made to broaden the knowledge regarding murine leprosy in members of the murine family other than the rat (rattus norvegics norvegics, rattus rattus alexandrinus, rattus rattus rattus).
The animals investigated were the mouse, hamster, wild members of the murine family, guinea pig, rabbit, cat and monkey.
The following conclusions were reached.
1) Special caution should be exercised in conducting experiments on the animal transmission of the leprosy bacillus, especially latency of murine leprosy bacillus.
2) The finding that the latent murine leprosy bacillus is present not only in the rattus family but also in the mouse and wild muridae, supplements the report of Nishimura (1938) on the category of murine leprosy.
3) The results suggest that the belief that natural murine leprosy infection takes place by direct contact, must be revised.
4) It can be said that the finding that the skin of healthy experimental animals is contaminated by acid-fast organism affords some understanding of the yet unclarified natural phenomenon.

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The author had results as follows, on this studies.
1. Thiozamin showed some antibacterial action to Mycobacterium tuberculosis and BCG bacteria. The growth checking action of Thiozamin (1×10^-4M) for BCG bactera was about 33%.
2. Thiozamin had inhibitory effect upon the development of murine leprosy.
3. On examination of mechanism of inhibitory effects of acid-fast bacteria, the results were as follows.
i) The effect of Thiozamin to respiration of BCG bacteria was only 11.9% of inhibition ratio in 7.37×10^-4M.
ii) Thiozamin showed little effect on protein synthesis of BCG bacteria.
iii) It showed almost no effect on the ribosome of BCG.
4. The results of pharmacological examination were very weak poisonous.
Therefor, this compound is proved to be safe enough for the clinical test.

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[in Japanese]

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An aqueous suspension of M. lepraemurium (Hawaiian strain), prepared from the organs of mice previously inoculated with this bacillus before a long period of time, was inoculated intravenously and subcutaneously into the mice of ddN strains. These mice were killed and autopsied from time to time. The removed organs, lymph nodes and subcutaneous nodules were ground in the mortar. The most part of ground materials was inoculated onto the 1% egg yolk medium principally and also onto 3% Ogawa's egg media and 1% Ogawa's egg media. These media were incubated at 37°C for nearly 3 months. The reading was assumed positive when the colony-like products were observed macroscopically.
The following was the results: The material which showed most abundant growth of bacilli in the mice during 5-8 months, gives positive result in 14 cases of 22 (63.8%) using 1% egg yolk media, while only one positive case out of 4 using 3% Ogawa's egg media. No positive case was found in 1% Ogawa's egg media. The colony-like products appeared to be a R-Type with somewhat moist nature and showed a very thin yellowish tint. We have succeeded so far in obtaining four successive cultures. The growth was very slow and almost took 2-3 months until the definite growth was assured. A smear specimen displayed well-stained acid-fast bacilli, among them also many elongated ones. These bacilli grew only at 37°C but failed to grow either at 22°C or 45°C. Reproduction test of these bacilli to the mice was favorable. Such a property is identical in every isolated bacilli.

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