On the antibacterial action of cultures of a penicillium, with special reference to their use in the isolation of B. influenzae. 1929.

1. A certain type of penicillium produces in culture a powerful antibacterial substance. The antibacterial power of the culture reaches its maximum in about 7 days at 20o C. and after 10 days diminishes until it has almost disappeared in 4 weeks. 2. The best medium found for the production of the antibacterial substance has been ordinary nutrient broth. 3. The active agent is readily filterable and the name has been given to filtrates of broth cultures of the mould. 4. Penicillin loses most of its power after 10 to 14 days at room temperature but can be preserved longer by neutralization. 5. The active agent is not destroyed by boiling for a few minutes but in alkaline solution boiling for 1 hour markedly reduces the power. Autoclaving for 20 minutes at 115o C. practically destroys it. It is soluble in alcohol but insoluble in ether or chloroform. 6. The action is very marked on the pyogenic cocci and the diphtheria group of bacilli. Many bacteria are quite insensitive, e.g. the coli-typhoid group, the influenza-bacillus group, and the enterococcus. 7. Penicillin is non-toxic to animals in enormous doses and is non-irritant. It doses not interfere with leucocytic function to a greater degree than does ordinary broth. 8. It is suggested that it may be an efficient antiseptic for application to, or injection into, areas infected with penicillin-sensitive microbes. 9. The use of penicillin on culture plates renders obvious many bacterial inhibitions which are not very evident in ordinary cultures. 10. Its value as an aid to the isolation of B. influenzae has been demonstrated.