18 MASS. EXPERIMENT STATION BULLETIN 449 



sterilized, and their survival in the soils is determined by accepted cultural pro- 

 cedures. The work is still in a preliminary stage, but results indicate that the 

 organism survives for only a few weeks under optimum conditions of moisture 

 and temperature. The results of the study reported in Bui. 441, and of an earlier 

 one (Study of septic tank efficiency, Mass. Expt. Sta. Bui. 436, p. 17, 1946), 

 have been published as a Station bulletin (Mass. Expt. Sta. Bui. 446). 



Bacteriological Study of Sewage Sludge. (James E. Fuller.) Previous ex- 

 perience in this laboratory had shown that Escherichia coli from sewage disap- 

 pears in a comparatively short time when sludge from a sewage disposal plant 

 is put onto a sand filter bed. The present study was undertaken to determine 

 the reasons for this disappearance and thus to provide some basic information 

 concerning the physiology of E. coli and its relation to its environment. The 

 results will be correlated with those obtained from the study of the soils of septic 

 tank disposal fields. 



To date two possible causes have been considered that might be responsible 

 for the disappearance of E. coli from sludge. The first was the presence of some 

 antagonistic biological factor such as bacteriophage or antibiotic substances 

 produced by associated microorganisms in sludge. Results failed to indicate any 

 such factor. The other possibility was that other microorganisms might offer 

 competition, especially for nutriment, with which E. coli cannot compete suc- 

 cessfully' in sludge. E. coli is a normal inhabitant of the human intestine where 

 it has optimum temperature and easily utilizable simple organic sources ot carbon 

 and nitrogen. When sludge was placed on a sand filter in the laboratory and 

 held at room temperature, E. coli disappeared after 14 days, while Aerobacter 

 aerogenes and other soil types of coliform bacteria persisted. At body temperature 

 (37° C), E. coli survived up to 56 days, and A. aerogenes survived much longer 

 This suggested a temperature influence, since E. coli is accustomed to the temper 

 ature of the human bod}'. When organic food substances (dextrose and peptone) 

 were added to sludge, E. coli survived for 21 days, whereas it had disappeared in 

 14 days without the added nutriment. Sludge, from which- E. coli had disap- 

 peared, was sterilized in an autoclave to destroy competing microorganisms. 

 E. coli was inoculated into the sterile sludge and has survived for 42 daj's. These 

 results all favor the competition theory as an explanation of the disappearance 

 of E. coli from sludge. 



Effect of Volatile Disinfectants on Survival of Microflora in Soil. (Charles 

 Hurwitz and Frank H. Dalton.) These studies were undertaken to provide a 

 method for sterilizing soil for laboratory studies which would permit subsequent 

 removal of the sterilizing agent and would cause a minimum of change in the 

 soil itself. A sealed jar containing the soil sample was evacuated and the atmos- 

 phere saturated with one of the following volatile disinfectants: chloroform, 

 hydrogen cyanide, chloropicrin, formaldehyde, and ethylene oxide. The rate 

 of survival of the soil microflora was determined by plate counts and by broth- 

 culture inoculation techniques. Ethylene oxide sterilized the soil after 11 hours 

 exposure, formaldehyde after 3 days, and chloropicrin after 8 days. Hydrogen 

 cyanide and chloroiorm decreased the numbers of viable microorganisms but did 

 not sterilize the soil after 8 days exposure. 



The extractability of copper and manganese from the soil with ammonuim 

 acetate was used as an indication of changes brought about in the soil as a result 

 of exposure to the disinfectants. Contact of the soil with formaldehyde caused 

 a 187 percent increase in extractable copper. With ethylene oxide the increase 

 was 309 percent; and with chloropicrin, 444 percent. Extract£.ble manganese 



