Apparently the extracellular protease of S. marcescens is present in protein- or protein derivative-free media only when the conditions favor an abundant growth and bacterial conglomerates are formed, which possibly could be explained by assuming that the proteins of dead bacteria or proteic metabolic products act as inducers of protease formation.

Dilute solutions of gelatin induce the production of proteolytic activity after a short period of time and its rapid increase before the initial number of bacteria has been duplicated.

Calcium is necessary to preserve the activity of the enzyme formed in synthetic media but not that produced in gelatin.

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