McKinley and Soule1 reported the successful cultivation of Mycobacterium leprae, obtained from Puerto Rican lepers, on several culture media. Subsequent reports were made by Soule and McKinley2, 3 when their nonchromogenic strain of acid-fast bacilli, believed to be the true Mycobacterium leprae, had been carried through the eighth and sixteenth generations respectively, the latter representing cultivation over a period of 18 months. Experimental protocols were also presented dealing with suggestive experimental lesions produced in 2 species of monkeys. In the cultivation work it was apparent that the leprosy microbe was maintained on artificial media with greater difficulty with each generation or transfer. In the sixteenth generation, so-called, after the organism had been on artificial media for some 18 months, only 2 definitely positive cultures resulted. One of these cultures has been employed in an attempt to ascertain better methods of cultivation.A logical procedure was to attempt cultivation in e...