16 MASS. EXPERIMENT STATION BULLETIN 305 



growth. In testing acid soils, such as those of this vicinity, it is customary to 

 add an excess of calcium carbonate to the soil to provide a reaction satisfactory 

 for Azotobacter growth. Perhaps the calcium may combine with the phosphorus 

 of the soil to fotm insoluble tricalcic phosphate which would not support Azoto- 

 bacter growth. This possibility is being investigated. 



Calcium Metabolism of Nitrogen-Fixing Bacteria. (J. E. Fuller.) This is 

 a new project begun in the spring of 1933. The object is to determine whether 

 calcium salts are important in the metabolism of bacteria except as regulators 

 of reaction in the substrata. At present the study is limited to a consideration 

 of the metabolism of Azotobacter. A medium free from calcium has been devised 

 which produces more fixed nitrogen in Azotobacter cultures than is obtained on 

 Ashby's Medium. Suitable reaction in the medium is obtained by the use of 

 di-potassium phosphate. The addition of calcium carbonate in several concen- 

 trations has not resulted in greater quantities of nitrogen being fixed by Azotobacter 

 cultures than when the calcium-free medium is employed. Care has been taken, 

 by the use of analyzed chemicals, to obtain a medium which is free from all 

 calcium except that which is purposely added. 



Biological Studies of Bacteria of the Coli-Aerogenes Group. (J. E. Fuller.) 

 This is another new project, the purpose of which is to investigate the physiology 

 of, and the influence of environment on, members of the Coli-Aerogenes group of 

 bacteria in the effort to interpret more satisfactorily the results of bacteriological 

 examinations jof water and milk. It is proposed to determine, if possible, whether 

 bacteria of this group having different physiological reactions are in reality 

 different species, or merely temporary variants produced by environment. The 

 study has just been started and the time to date has been spent in the collection 

 and purification of cultures. 



Laboratory Service. (R. L. France.) Following is a list of the number and 

 types of examinations made in the laboratory during the past year: 



Milk (bacteria counts) 1,087 



Water 120 



Miscellaneous: 



Butterfat 309 



Solids 18 



Stringiness 1 



Total 1,535 



The total number of analyses shows a slight increase over the previous year. 

 The milk phase of service is proving of great value to producers, dairymen and 

 local inspectors throughout the Valle\ . 



The number of water analyses compares favorably with the previous year. 

 Through the cooperation of the Engineering Specialist of the Extension Service, 

 it will be possible in the future to make a sanitary survey of polluted private 

 water supplies. By this means constructive suggestions as to the elimination 

 of the pollution wnll be available, thus giving a most complete service in this field. 



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

 requesting them for inoculation of leguminous plants. 



The Indol Tolerance of the Coli-Aerogenes Group of Bacteria as a Possible 

 Means of Differentiating Fecal and Non-Fecal Strains Occurring in Drinking 

 Water Supplies. (R. L. France.) Results to date indicate a very definite 



