The Determination of L.D.50 and Its Sampling Error in Bio-Assay.

The formation of clavacin in the culture medium corresponded with the maximum growth, as measured by the complete consumption of the sugar in the medium and by maximum nitrogen utilization. After the maximum antibacterial activity had been reached in the medium, the activity of the clavacin was rapidly destroyed. This was found to be due not to the disappearance of the substance itself from the medium but to its inactivation. Only six of the fifteen strains of A. clavatus produced considerable amounts of clavacin. The remaining nine strains gave only traces of the active substance. The clavacin produced by the different active strains of A. clavatus was found to be the same biologically, as shown by its activity against different bacteria, and apparently the same chemically, as shown bv solubility studies and chemical behavior. Attention is directed to too hasty generalizations concerning the ability of certain fungus species to produce antibacterial substances, based upon the study of single strains of a given organism.