1. The pretreatment induction method of studying the formation of ß-galactosidase in E. coli B has been described.

2. It has been found that E. coli B cells have their maximum capacity to form ß-galactosidase, in response to a constant induction stimulus, when they are in the stationary phase of the growth cycle.

3. The concentration of inductor, the nature of the nitrogen source, the duration of the assimilatory phase, oxygen tension, and temperature are factors which affect, and may limit, the rate of ß-galactosidase formation.

4. When limitations imposed by these factors were removed, the time course of induced ß-galactosidase formation was strictly linear from the onset.

5. The implications of this finding were discussed and a new theory of the mechanism of enzyme formation has been proposed.

6. A very satisfactory method of synthesis of ortho-nitrophenol-α-D-galactoside has been described. This substance is a suitable chromogenic substrate for the specific determination of α-galactosidase activity.

7. Preliminary experiments using this substrate have confirmed the results of respiration studies and shown that in E. coli B α-galactosidase formation may be induced by ß- as well as by α-galactosides.

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