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Nagler (1939) and Seiffert (1939) independently described the production of opalescence in huiman serum by type A Clostridium welchii toxin. This reaction was found to be correlated with the lethal action of the exotoxin and inhibited by specific immune serum. MacFarlane and Knight (1941), in an analysis of the chemical reactions involved in this phenomenon, demonstrated that the a fraction was the responsible component of the toxin and that it was a lecithinase. A simple method for the titration of this lecithinase activity using filtered egg yolk lecithovitellin (LV) was developed by van Heyningen (1941). As a result of these and other investigations, convenient in vitro methods for estimating the potency of type A C. welchii toxins are available and the titrations of antibody responses following infection or immunization have been simplified. It was noted by Nagler (1939), at the time of his initial observations, that, unlike human serum, the production of opalescence by C. welchii toxin did not occur with most animal serum. Several explanations of this nonreactivity of normal animal serum are possible: (1) lack of substrate in available form, (2) lack of necessary coenzymes, (3) presence of specific immune bodies, and (4) presence of naturally occurring nonspecific inhibitory substances. The experimental evidence presented here appears to support the last of these explanations.

NONSPECIFIC INHIBITION OF THE LECITHINASE ACTIVITY OF TYPE A CLOSTRIDIUM WELCHII TOXIN