Pure cultures of an acid-fast bacillus were cultivated upon special media from the human tissues in four cases of leprosy. The nature of the growth, morphological characters and tinctorial properties do not differ for any of the cultures and correspond closely to the bacilli in the human leprous tubercles.

That the bacillus of leprosy will multiply and continue to do so indefinitely outside of the animal body was first demonstrated by Clegg who cultivated an acid-fast organism from leprosy tissue in the presence of ameba and their symbiotics. Not only have I been able to confirm Clegg's work, but in addition I have succeeded in growing the bacillus in pure culture and in reproducing the disease in the Japanese dancing mouse, thereby establishing its identity. This species of animal acquires the infection in four to six weeks after intraperitoneal or subcutaneous inoculation with either emulsions of fresh leprous tissue or the pure cultures of B. lepræ. Comparatively few bacilli are necessary to infect the mouse; and the mode of inoculation does not seem to make any appreciable difference in respect to the nature and time of development of the lesion.

The experimental lesions are proliferative in character and identical with those in the human subject. Macroscopically they appear as glistening, white nodules which, in the early stages of development, resemble miliary tubercles.

In my experience neither the cultures nor the bacilli directly from the human tissues have shown any evidence of multiplication or given rise to lesions when injected into the ordinary laboratory animals such as guinea pigs, rabbits, gray and white mice and rats, although repeated attempts have been made to infect these animals.

B. lepræ will not only multiply but it will colonize on a plain agar medium seeded with a pure culture of encysted ameba (Plate LVIII, Fig. 5), and upon an agar or banana medium prepared with a I per cent. solution of cystein and tryptophane. Colonization occurs in the form of glistening, white colonies, one to two millimeters in diameter, in from one to two months incubation.

The bacilli in cultures are at all times acid-fast and differ only in morphology from those of the tissues in that they exhibit a greater variation in the distribution of the chromatin and are longer and more distinctly curved.

To prove that the cultures obtained from the human tissues of these four cases are leprosy bacilli and not some other acid-fast species, the following facts are offered: (1) the growth features are distinctive and multiplication takes place only under special conditions of temperature and medium; (2) the complete correspondence in tinctorial properties and similarity in morphology to those in the tissues; (3) the failure to multiply or produce lesions in the common laboratory animals; and (4) the growth of the bacilli and the production of typical leprous lesions in the Japanese dancing mouse.

The successful cultivation of B. lepræ and the fact that the cultures retain pathogenic properties are of commanding importance in respect to a possible production of an artificial immune serum for combating the infection in man. Work along this interesting line is already in progress in our laboratories.

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