SUMMARY: Microbes were grown on microscope slides so that the growth could readily be observed by phase-contrast microscopy.

, grown on agar containing penicillin, undergoes extraordinary morphological changes which vary with the temperature of incubation, the concentration of the penicillin, the concentration of the agar and the presence of small amounts of fluid between the agar and the cover-slip. The bacilli may divide normally once or twice into elements that grow without dividing and which may develop into fantastically shaped thread or swollen forms. In high concentrations of penicillin the fantastic shapes are obtained by enlargement without division. At first the nuclei divide as in normal organisms. The thread forms have condensed nuclei arranged in alternating pattern along the side of the cells. In the swellings there may be either nuclear material filling the cells, a condensed central mass or a reticulum. When vacuoles are present these displace the nuclear material.

When the misshapen organisms are transferred to a medium free from penicillin and containing penicillinase they divide, forming normal bacilli. Many of the swollen elements burst and disappear.

The motility of the greatly enlarged organisms is sluggish, and flagellar movement can clearly be observed by phase contrast. The movement of the flagella of the organisms responds readily to radiant heat, and a careful study of these movements makes it impossible to accept Pijper's contention that bacterial motility is due entirely to undulatory movements of the body and that the flagella are merely mucoid strands cast off as the result of motility.

The flagella were demonstrated in the large forms by fixing the culture through the agar for several days, detaching the agar and staining the cover-slip, which carries the fixed colony, with a saturated watery solution of night blue. The nuclei were shown by treating films with hot nitric acid, washing and staining first with cresyl blue then Leishman's stain.


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