ANNUAL REPORT, 1942 15 



DEPARTMENT OF BACTERIOLOGY 

 Leon A. Bradley in Charge 



Nitrification in Soils Containing Plant Residues of Varying Lignin Content. 



(James E. Fuller, cooperating with the Agronomy Department.) This investi- 

 gation, so far as the field work is concerned, is obviously seasonal and consequently 

 proceeds slowly. A preliminary' statement was made in the 1941 report from this 

 Department (Mass. Agr. Expt. Sta. Bui. 388: 19, 1942). The crops employed 

 were millet, rye, wheat, sudan grass, sorghum, corn, oats, buckwheat, barley, 

 rape, artichoke, tobacco, and sunflower. There were six plots with all of the crops 

 in each, except the sunflower, which was alternated with fallow strips. The 

 crops were grown and then plowed under. The following season tobacco was 

 grown on the plots, and during that season three series of soil samples were col- 

 lected — one early in the season before the tobacco was planted, another in mid- 

 summer, and the third in the early autumn after the tobacco had been h?rvested. 

 These samples were tested for their ability to nitrify dried blood and ammonium 

 sulfate. 



The general tendency seemed to be that the capacity of the soil to nitrify dried 

 blood declined in mid-summer as compared to the spring, and then recovered to 

 some extent later in the season. There was considerable variation among the 

 different plots, and no definite relationship could be noted between the variety 

 of crop and the nitrifying capacity of the soil of the plot. The ability of the 

 soils to nitrify ammonium sulfate declined markedly, in general, when the early 

 and mid-season samples were compared, and there was little recovery of activity 

 when the late-season samples were analyzed. 



The nitrification results are being compared with the production and the grade 

 and crop indices of tobacco grown on the plots. No relationship has been noted, 

 but further study of the data is being made. 



The Determination of the Sanitary Quality of Drinking Utensils. (Ralph L. 

 France and James E. Fuller.) This project had been carried on b}' France, and 

 after he entered the armed service of the country the work was taken over by 

 Fuller, who completed some unfinished work and prepared a report. The results 

 may be summarized as follows: A wet swab with excess moisture squeezed out 

 was more effective than a dr\- or a moist swab for removing bacteria from used 

 drinking glasses. A diluting fluid containing a phosphate (Butterfield's phosphate) 

 was more effective than distilled water or physiological salt solution for preserving 

 the viability of bacteria on swabs when they had to be held for some time before 

 plates were made. When swabs had to be held for several hours before plates 

 were made, it was found that chilling the containers with ice helped materially in 

 preventing loss of viability of the bacteria. A yeast-dextrose medium smiilar to 

 that used for the Standard-Methods procedure for plating milk samples gave 

 good recovery of bacteria for swabs. Practical examinations were made of local 

 establishments serving food and drink. 



Bacteriological Study of Chocolate Milk. (James E. Fuller and R. W. Swan- 

 son, in cooperation with W. S. Mueller of the Department of Dairy Industry.) 

 This study has been completed and the results published. They may be sum- 

 marized as follows: The addition of chocolate syrups or cocoa powders inhibited 

 the growth of bacteria as compared with growth in the milk without the powders 

 or syrups. Even though the bacterial content of some of the powders and syrups 

 was high, the resultant growth of bacteria in chocolate milk made from these 

 powders or syrups was not nearly as great as was anticipated. Experiments 

 indicated that the tannic substances in the chocolate or cocoa were responsible for 

 the inhibition of bacterial growth. 



