SUMMARY: Various methods of preparing microcultures with liquids (hanging-drop) and solids (collodion, cellophan, agar) were compared with respect to the mode of growth of the test organism on a complex nutrient substrate. Cell division was promoted in general by lower temperatures, by ageing, by lack of humidity in solid cultures, by the action of surface tension operating in the more convex droplets, and by the addition of surface-active agents to liquid media. By varying the carbon sources in chemically defined media it was found that starch, glycogen, and to some extent glucose, favoured filamentation, i.e. retarded or inhibited cell division, in comparison with a considerable variety of other sugars. Of the nitrogenous sources, nitrate resulted in relatively poor growth mainly composed of mycelial aggregates that later exhibited cell division to the extreme limits; ammonium salts yielded more profuse filamentous growth with less subdivision; certain single amino acids induced a more uniform development of short rods: while casein hydrolysate commonly produced a variety of cell elements showing subdivision in all stages. Single cell isolates were used throughout, and the mode of growth was studied by means of phase-contrast and electron microscopy.

A cultural description of the test organism, , n.sp. is given at the end of the paper.


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