16 MASS. EXPERIMENT STATION BULLETIN 428 



Relation of Chloramine-Resistant Bacteria to Milk Supplies. (James E. 

 Fuller.) Previously published results (J. New England Water Works Assoc, 

 58: 89-100, 1944) showed a substantial increase in the number of positive pre- 

 sumptive tests (gas production in lactose broth) obtained in routine testing of 

 the water after the chlorine-ammonia treatment was begun. These tests, how- 

 ever, could not be confirmed; that is, they were false presumptiv^e tests. During 

 the past year studies have been made to determine the cause of the false presump- 

 tive tests. Results follow: 



1. Numbers of Gram-negative bacteria have been isolated that resemble 

 coliform bacteria except for their failure to confirm, that is, to produce gas in 

 lactose broth within 48 hours of incubation at 37° C. 2. By passing the cultures 

 through successive tubes of lactose broth, the ability to produce gas within 48 

 hours was built up in a number of them. 3. By combining the cultures with 

 one another, or with certain Gram-positive aerobic spore-forming cultures also 

 isolated from the water, it was possible to obtain positive presumptive tests. 



The conclusion was that the false presumptive tests obtained from the water 

 supply are caused by coliform bacteria whose fermentative capacity had been so 

 weakened by environment that they were unable alone to produce gas from 

 lactose, but could do it when combined with other cultures. This study has 

 been accepted for publication in the Journal of the New England Water Works 

 Association for September, 1945. 



The last phase of the study, now under way, is to investigate the possible effect 

 of these bacteria on milk supplies. Some work has been done to determine their 

 rate of multiplication in milk at several temperatures ranging from room tem- 

 perature to that of normal refrigeration in an electric refrigerator. The produc- 

 tion of acid and curd in milk under these conditions is also being investigated.- 

 W^ork on this phase of the problem has not progressed sufficiently to warrant any 

 statement of results at this time. 



Study of Septic Tank Efficiency. (James E. Fuller.) A preliminary statement 

 has been made (Mass. Agr. Expt. Sta. Bui. 417, 1944, p. 17) explaining the 

 origin of this project as a cooperative study with the State Board of Health 

 Division of Engineering. After the Department of Bacteriology took over the 

 project, a part of the tank installation was rebuilt, with the cooperation of the 

 Department of Engineering of the Experiment Station, to eliminate certain 

 faulty features of the original design. 



It has not been possible to operate the project continuously, partly because 

 the dormitor}^ that supplies sewage to the tank has been occupied by pre-aviation 

 cadets on a "here today and gone tomorrow" basis, and partly because the 

 installation is not housed, with the result that deep snow and very cold weather 

 necessitated suspension of operation in mid-winter of 1944-45. However, some 

 results have been obtained. 



The main object of the project was to study the effect of retention period on 

 the efficiency of the tank in digesting the sewage. The tank has three compart- 

 ments which receive sewage at rates that provide retention periods of 24 hours, 

 12 hours, and 8 hours respectively. The tank was put into operation in late 

 August, 1944. Scum formed rapidly in the 12-hour and 8-hour compartments, 

 and the outlets from both were plugged up solidly by early December with scum 

 about 8 inches thick. The scum in the 24-hour compartment formed gradually 

 and more normally and was about 2 inches thick when operation was suspended. 



Bacteriological studies of the effluent showed that the coliform bacteria re- 

 covered at the beginning of operation were mostly typical Escherichia coli, while 

 after about six weeks the type changed to Citrobacter which is a member of the 

 coliform group but not so indicative of immediate fecal pollution as E. coli. 



