[Studies on murine leprosy bacilli].

In preceding papers, several reports were made on the in vitro cultivation of M. lepraemurium. This paper describes some further observations on the primary and secondary cultures of this organism.1. Gross appearance and transplantability of primary isolates.Macroscopically the primary cultures of M. lepraemurium isolated on the egg yolk slant may be divided into three: (i) discrete colonial growth; (ii) growth on a debris of the tissue homogenate inoculated, either colonial or membraneous; and (iii) membraneous growth. Although each of the growth was obtained from various kinds of materials, cultures from the tissues with a very large amount of bacilli had a tendency to develop into (ii) or (iii), and the ones from the tissues with a smaller amount into (i).The positive rate on the first passage of the primary isolates varied over a wide range depending on the type of growth; namely, the rate of those cultures which appeared as (i) colonial growth, (ii) colonial or membraneous growth on the debris, and (iii) membraneous growth was 84%, 50% and 28% respectively.2. Occurrence of smooth variants during serial passages.Cultures of M. lepraemurium on the egg yolk slant are originally rough but during serial passages occasionally become smooth. Retrospective analysis on the occurrence of smooth variants was made on a total of 2, 118 subcultures of Hawaiian strain and of 257 subcultures of Keishicho strain in the courses of their respective twenty and sixteen passages. Smooth variants occurred in the 7th to the 14th passages and the rate of occurrence was found to be 0.7% and 2.3% respectively. Gross appearance of the primary isolate and the kind of tissue material used for primary isolation bore no relation to the occurrence of smooth variants.The in vitro characteristics of smooth variants were the same as those of the original rough ones, except that the formers were more easily emulsified.