M. lepraemurium Hawaii was grown on the modified Ogawa's yolk medium at 32-37C but was not at 45C. Colonies were rough and creamy white. Pigment prodution in dark and pigmentation after exposure to light were not observed.
Amidase tests were performed with 12 substrates; acetamide, benzamide, urea, isonicotinamide, nicotinamide, pyr azinamide, salicylamide, allantoin, succinamide, malonamide, n-capramide and n-caprylamide. Amidase activities of nicotinamide, pyrazinamide, n-capramide and n-caprylamide were observed in M. lepraemrium, but those of the other eight substrates were not detected (Table. 1).
In vivo bacilli of M. lepraemurium Hawaii grown in C3H mouse and in vitro bacilli of M. avium, M. intracellulare and M. xenopi grown on Ogawa's egg medium had the same amidase activities as that of in vitro M. lepraemurium Hawaii (Table. 1 and 2).
Niacin test (-), catalase activity (+), heat stable catalase (-), nitrate reduction (-), heat stable phosphatase (-), Tween 80 hydrolysis (-), arylsulfatase (-), diamine oxidase (-) and insusceptibility to ethambutol (5 μg/ml) were mostly the same as the reports of Ogawa or Koseki.
From the facts described above, we may conclude that M. lepraemurium has the most similar characterisitics to M. avium and that the heat stable catalase activity and multiplicity at 45C can be used to differentiate among M. lepraemurium and M. avium.

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It was demonstrated that M. lepraemurium which were cultivated for 223 days at 30°C by bacillary suspended method and for 172 days by slide culture method, had the in-fectious abilities to susceptible mice. In both cases, the procedure of refreshing culture medium resulted stimulation of the growth of bacilli. In the case of slide culture method, it could be noted that the infectious abilities of the cultivated bacilli depended upon the number of living organisms, because the growth of bacilli was stimulated by a slide transfer procedure. On the other hand, no pathogenicity was demonstrated when the bacilli were cultivated for 64 days as the control in the EKP medium under the same condition.
However, the quantitative observation about a relationship between the growth rate of bacilli and the grade of pathogenicity illustrated that multiplied bacilli had the reduced pathogenicities comparing to that of starting material.

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Stabilities of the NC-5 and NC-7 medium for the growth of M. lepraemurium were studied. For this purpose, these media were kept at 37°C and 4°C for one and two months. Using slide culture method, M. lepraemurium were cultivated in a freshly prepared medium and the preserved media. In order to see the stabilities of the preserved media, the multiplication of M. lepraemurium in the preserved medium was compared to that in a freshly prepared one. The results obtained show that the ba- cilli multiplied equally in both freshly prepared and preserved media in the case of NC-5 medium, and that, in the NC-7 medium, the dominant growth was observed in the medium which was kept for one month at 37°C, and the inferior growth was seen in the medium preserved for two months at 37°C. Therefore, it could be concluded that the NC-5 medium would be very stable for use.

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The experiments of the factors influencing the growth of M. lepraemurium smeared on slides and cultivated in NC-5 medium were carried out as following ways :
1. Slide-transfer group: the group which a smeared slide was transferred to a freshly prepared medium at a definite interval.
2. Air-exposure group: the group which a slide was just taken out and put again in the same medium at a definite interval.
3. Stopper-opening group: the group which a rubber stopper was just taken out andsealed again at a definite interval.
4. Control: no treated group.
The growths of bacilli treated with the four procedures were compared. The most remarkable growth was observed in the case of the air-exposure group, and the inferior growth was obtained in control group. From the results, it could be presumed that periodical exchange of air in sealed culture medium might be necessary for the growth of bacilli.
In the experiments of bacillary cultivation, the suspensions of bacilli were inoculated and cultivated in 50 ml of NC-5 medium, which were distributed to a 50 ml-flask, 100 ml-flask, and 200 ml-flask, respectively. After two months' cultivation at 30°C, bacterial cells were collected by centrifugation and the wet weights of sediments were measured. The best yield of bacterial cells was obtained when the bacilli were cultivated in a 50 ml-flask, and the poor yield was observed in the case of a 200 ml-flask. Therefore, it would be presumed that M. lepraemurium might multiply under a slightly anaerobic condition, rather than aerobic one.
From the results of two experiments mentioned above, it could be emphasized that the growth of M. lepraemurium would unexpectedly depend upon the influence of air.

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