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Kindler et al. (1956) reported that a strain of Clostridium parabotulinum type A synthesized large quantities of toxin in a medium where cell multiplication was inhibited by high concentrations of penicillin. This interpretation of synthesis de novo of protein was based on the observations that the toxicity of the extracellular fluids increased in the absence of cell multiplication. It is a well established fact that growth of Clostridium botulinum reaches a maximum and is followed very rapidly by a period of cellular degeneration and autolysis which results in the liberation of large quantities of toxin (Boroff, 1955; Kindler et al., 1955; Bonventre and Kempe, 1959a). At the end of the exponential growth phase the sum of the intracellular and extracellular toxin is approximately 10 per cent of that found in the culture filtrates which are allowed to incubate until autolysis is complete (Bonventre and Kempe, 1960). If synthesis de novo of protein is responsible for the increase in toxicity noted during the autolytic process then it must be assumed that 90 per cent of the toxin is synthesized during a period of cellular degeneration. Since this period in the life of microorganisms is usually characterized by catabolic rather than anabolic processes, the synthesis of such large amounts of protein would be a rather unique biological situation. In an attempt to investigate this phenomenon further, mechanisms other than synthesis de novo were considered. It has been known for some time that some of the protein bacterial toxins can be altered by proteolytic enzymes so that their activity is increased (Turner and Rodwell, 1943; Cohen et al., 1 Present address: Department of Microbiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio. Part of this work was carried out during the tenure by one of us (P. F. B.) of the Novy Research Fellowship, Department of Bacteriology, University of Michigan.

PHYSIOLOGY OF TOXIN PRODUCTION BYCLOSTRIDIUM BOTULINUMTYPES A AND B I