ANNUAL REPORT, 1946-47 15 



DEPARTMENT OF BACTERIOLOGY 

 Leon A. Bradley in Charge 



Septic Tank Studies. (James E. Fuller.) This is a continuation of work 

 previously reported (Mass. Expt. Sta. Bui. 436, p. 17, 1946). This study was 

 concerned with the penetration of sewage-type coliform bacteria into the soil of 

 disposal fields receiving sewage effluents from three septic tanks which repre- 

 sented three retention periods for raw sewage: 8, 12, and ?4 hours. The soil 

 samples were examined to determine their coliform indices by the conventional 

 procedure of gas production in lactose broth, as outlined in the Standard Methods 

 of Water Analysis (American Public Health Assn.). Organisms isolated from 

 positive fermentation tests were studied to determine their relationship to sewage- 

 type coliform bacteria (Escherichia colt). Results showed almost no sewage-type 

 organisms in the soil, in spite of the fact that the flow from the 8-hour retention 

 tank was so rapid that soil surrounding the disposal line was frequently saturated 

 with moisture. Organisms isolated were, for the most part, the same as those 

 isolated from soil (of the same type) that did not receive septic-tank effluent. 

 Two conclusions resulted from the study: (1) the length of retention of sewage 

 in the tanks did not influence the results obtained from the soil, and (2) the 

 sewage-type coliform bacteria isolated from the raw effluent either did not pene- 

 trate into the soil or did not survive. Further study is planned to investigate 

 the survival of sewage-type coliform bacteria in soil under different conditions. 



Bactericidal Properties of Surface-active Agents. (James E. Fuller.) It was 

 reported previously (Mass. Expt. Sta. Bui. 436, p. 17, 1946) that preliminary 

 tests had been made on 42 surface-active agents to determine their germicidal 

 efficiency. Several of these agents, representing three chemical groups, were 

 chosen for further study of their germicidal properties, in different concentrations, 

 against two representative t^'pes of bacteria, Escherichia coli and Staphylococcus 

 aureus. The chemical groups represented were quaternary ammonium com- 

 pounds, phosphonium compounds, and aliphatic sulphonates. Usually a certain 

 concentration is recommended for the use of an agent. Results of the experi- 

 ments indicated that the effectiveness of the agents varied for the different 

 bacterial species, and that a formula could be derived for each agent showing the 

 relationship of concentration of the agent and dosage time for any given bacterial 

 species. The results of the experiments indicated that the agents could be made 

 more widely useful if directions for their application were made more flexible, 

 and economy of materials might result if weaker concentrations were employed 

 where speed of disinfecting action is not important or necessary. 



Microbiological Fixation of Copper in Soil. (Charles Hurwitz.) This study 

 was undertaken to determine the effect of the soil microorganisms on the avail- 

 ability of the soil supply of copper to higher plants. Copper leached from the 

 soil by neutral, normal ammonium acetate is considered available. Leachable 

 copper was found to be greatly increased by an unknown soluble component of 

 oat straw and alfalfa meal when either sodium chloride or ammonium acetate 

 was used as the leaching solution, the effect being found in both Merrimac sandy 

 loam and Dunkirk silty clay loam. This unknown soluble component is decom- 

 posed by soil microorganisms in about 14 days at 29° C, 37° C, and 45° C, no 

 marked differences being observed at any of these temperatures. At 2° C, no 

 decomposition of the soluble component occurred in 21 days, but when this soil 

 was placed at 29° C, decoinposition proceeded as before. Work is in progress 

 now to characterize this unknown soluble component and to determine its agri- 

 cultural significance. 



