Six strains of mycobacteria,—three human strains, Saranac H-37, T. S., and No. 90, a bovine strain, B-1, a smegma strain, No. 74, and a Saranac strain of B. phlei,—have been made to grow as non-acid-fast organisms by the addition to the culture media of a filtered extract of the chromogenic H-37 strain of B. tuberculosis. The action of the extract produced acceleration of growth of the treated culture, followed by macroscopic and microscopic changes, and differentiation into non-acid-fast forms. The bacterial forms grown from these treated cultures were pleomorphic, usually consisting of cocci and small rods; but branching forms and spore-like bodies also developed.

The sterility of the extract causing the changes was demonstrated by frequent control inoculations on various media, including Kendall's K medium; and autoclaved extracts had the same effects as non-autoclaved.

After transfer to media suitable for acid growths four of the strains reverted not only to acid-fastness but to their original cultural characteristics, providing evidence that the non-acid-fast forms were specific for the strain.

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