ANNUAL REPORT, 1945-46 17 



multiplying in milk and spoiling it, even at the normal operating temperature of 

 an electric refrigerator. All of the cultures were killed effectively by pasteuriza- 

 tion except those that formed spores. These was as expected. This project is 

 completed. 



Study of Septic Tank Efficiency. (James E. Fuller.) In this study three sep- 

 tic tanks of identical size were supplied with sewage from one of the college 

 dormitories. The rates of supply to the three tanks were so regulated that 

 sewage was retained in them 24 hours, as usually recommended, 12 hours, and 

 8 hours, respectively. The object was to determine whether the shorter reten- 

 tion periods would result in greater operating efficiency in the tanks. Results 

 showed that the conventional 24-hour retention was superior to the shorter 

 periods on the basis of the following evidence: (1) the coliform index of the 

 effluent was lower for the 24-hour period than for the shorter periods; (2) the 

 biochemical oxygen demand results favored the 24-hour period as compared with 

 the shorter periods; (3) at the end of three months of operation for two consecu- 

 tive seasons, the thickness of scum in the normal tank was about 2 inches; while 

 in the tanks with 12-hour and 8-hour retention periods, thicknesses of 11 and 13 

 inches respectively resulted, which would have plugged up the outlets of these 

 tanks if they had been constructed with the usual outlets. An extension of the 

 project was secured to permit a study of the permeation of coliform bacteria into 

 the soil of the disposal field, and of the accumulation of nitrates in the soil. This 

 work is in progress now. 



Effectiveness of Commercial Surface-active Agents for Use as Household 

 Cleansing Agents. (James E. Fuller.) Some 42 agents have been examined to 

 determine their germicidal power. About one-third of them were found to be 

 very effective, and several others were moderately effective. Experiments are 

 now under way to devise a procedure for evaluating the efficiency of these agents 

 on a sliding scale on the basis of variations of time and concentration, preparatory 

 to investigating the effect of organic matter, acids, and alkalis on the germicidal 

 power of the agents. 



Types of Microorganisms Involved in the Spoilage of Home-canned Foods. 



(Ralph L. France.) This is a new projedct an work has only been begun. To 

 date no results are available for report. 



Laboratory Service, July 1, 1945, to June 30, 1946. (James E. Fuller.) 



Milk samples, bacteria counts 171 



Ice cream samples, bacteria counts 76 



Water samples, bacteriological tests 140 



Total 387 



DEPARTMENT OF BOTANY 

 A. Vincent Osmun in Charge 



Diseases of Trees in Massachusetts. (M. A. McKenzie and A. Vincent 

 Osmun.) 



The Dutch Elm Disease Problem. As of July 1, 1946, the Dutch elm disease, 

 caused by the fungus Ceratostomella ulmi (Schwarz) Buisman, has been isolated 

 from 182 trees in 28 municipalities in Massachusetts, as follows: 



