ANNUAL REPORT, 1932 15 



This is an increase of 270 examinations over the previous year, due mostly to 

 bacterial and chemical examinations of milk. This phase of the service has in- 

 creased yearly, and the laboratory is providing a valuable service to milk pro- 

 ducers, dairymen and local health inspectors throughout the Valley. 



The number of water analyses has shown a decrease during the past year. This 

 is probably due to the fact that the laboratory is unable to make a sanitary survey 

 of the supplies examined. Without this survey it is impossible to offer construc- 

 tive suggestions in the care of polluted supplies. 



The stock of legume cultures has been kept intact and these were furnished to 

 farmers requesting them for inoculation of leguminous plants. 



Upon request of the Horticultural Manufactures Department bacterial exami- 

 nation of samples of a new baby food were made. 



Bacterial counts of milk samples held under different cooling methods were 

 made for the Dairy Department. 



The Indol Tolerance of the Colon-Aerogenes Group of Bacteria as a 

 Possible Means of Differentiating Fecal and Non-Fecal Strains Occurring 

 in Drinking-Water Supplies. (R. L. France.) Preliminary work on this proj- 

 ect has been completed and accepted for publication in the Journal of Bacteriology 

 under the title, "Bacterium coli in rural privately owned water supplies." 



The results obtained in this investigation suggest that dependence on the Stan- 

 dard Methods procedure alone for determining the sanitary quality of drinking 

 water, especially from privately owned supplies of unknown hi.story, results in 

 too many of the samples being condemned. The need of supplementary differen- 

 tial tests is indicated, but results do not justify the recommendation of any parti- 

 cular test or group of tests. 



In an effort to derive a satisfactory test, work is being done to determine the 

 indol tolerance of strains of the Colon-aerogenes group of bacteria. Results to 

 date do not justify any statement regarding sharp differences among strains. 



DEPARTMENT OF BOTANY 

 A. Vincent Osmun in Charge 



Black Root-Rot of Tobacco. (\V. L. Doran.) Tobacco was grown for the 

 tenth successive year in plots last limed in 1923. In 1932, there was no black root- 

 rot in plots not limed, the soil of which has a pH value of 5.2, but the disease was 

 moderately severe in adjacent limed plots, the soil of which has a pH value of 5.9. 

 The average yields of tobacco per acre in 1932 were 1906 pounds in plots not 

 limed and 1559 pounds, or 18 per cent less, in plots limed. The persistence of the 

 effects of lime on black root-rot and yields of tobacco is indicated by the fact that, 

 with lime last applied in 1923, loss in yield in limed plots (as compared with yield 

 in plots net limed) has been as follows: 10 per cent in 1924, 45 per cent in 

 1925, 43 per cent in 1926, 35 per cent in 1927, 23 per cent in 1929, 25 per cent in 

 1930, 16 per cent in 1931, and 18 per cent in 1932. The sorting record of the crop 

 of 1931 (the latest crop sorted) showed that lime applied in 1923 was still resulting 

 in impaired quality as well as reduced yields. The fire-holding capacity of the 

 crop of 1931 was not injured by lime, however. 



In pot experiments, infection of tobacco by Thielavia basicola (Berk, anil Br.) 

 2opf was much reduced or, more often, entirely prevented by ammonium thio- 

 cyanate applied to soil at the rate of 900 pounds per acre. This rate of application 

 was as effective in preventing infection as were heavier applications. It resulted, 

 however, in soil toxic to tobacco for 18 weeks, although not for 25 weeks, after 



