Summary: Protoplasts of grew well and divided in 1 % casein hydrolysate (enzymic) medium containing 0·5 -NaCl as the stabilizer. A fibrous layer of coat, possibly composed of murein, developed around the growing protoplast. A small protuberance then formed on the protoplast and grew until a symmetrical dumbbell-shaped body was formed. The coat did not develop around the ‘daughter’ protoplast.

Division was completely inhibited in the presence of penicillin, and a coat did not develop around the protoplast. Materials which might otherwise have formed the coat in the absence of penicillin were released into the medium.

After 12 h. of growth in the absence of penicillin, normal cell wall was formed around the cell, although reversion to bacillary form was not observed. The cells divided into 4 to 6 cells simultaneously by transverse septa, and intracellular membranous organelles (mesosomes) appeared within.


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