28 Director's Report of the 



of 43 Guernsey cows failed to show the close relationship between 

 infections of the udder with streptococci and the discharge of large 

 numbers of cells which has been claimed by some previous investi- 

 gators. The contradictory nature of the results obtained make it 

 increasingly probable that the discharge of these cells is not due 

 to a simple cause. 



This bulletin likewise reports the results of the studies which are 

 made to determine whether increasing the vacuum used in operating 

 mechanical milkers would have an effect upon the number of cells 

 discharged in the milk. The investigation was made because it 

 has been frequently thought that increased vacuums drew blood 

 from the interior of the udder, or at least caused an increased dis- 

 charge of cells. A six weeks' test where the vacuum was increased 

 from the normal of 14.5 inches to 19.5 inches failed to show any 

 effect on the cell content of the milk. A comparison between the 

 number of cells in the milk of machine-milked and hand-milked 

 cows in the Station herd showed somewhat fewer cells in the milk 

 of the machine-milked cows. 



Bacteria of frozen soil. — Observations made at the Cornell Uni- 

 versity Experiment Station a few years ago by one of the present 

 members of this Department have been confirmed and extended 

 by work at this Station. The original observation that the number 

 of bacteria in frozen soil is generally larger than in unfrozen soil 

 has been confirmed, and also it has been shown that this increase 

 is not due to the increase in soil moisture in the frozen soil nor to 

 a migration of bacteria to the surface layers from lower depths. 

 This makes it probable that the increase in number is due to an 

 actual growth of bacteria in frozen soil. Further studies on the 

 effect of seasonal changes on bacterial life are needed to explain 

 this fact and to determine its practical value, if any. The work 

 has been reported in Technical Bulletin No. 35. 



Cultural media for soil bacteriological ivork. — One of the most 

 serious handicaps in agricultural bacteriology is lack of precise 

 methods of work. Much of the present technique in soil bacteriology 

 consists of the crude methods characteristic of the earliest stages 

 of the development of a science or of technique taken from other 

 fields of bacteriology and applied to soil work without any careful 

 study of its efficiency in the new field. For these reasons it has 

 been necessary to make an extended study of the cultural methods 



