92 ABSTRACTS 



marked vigor. For a number of years we have been satisfied that 

 plain amniotic agar was a very nearly ideal medium for B. abortus 

 (Bang). 



Study of Effect of Dilution Water on Bacterial Suspensions. H. M. 



Weeter. 



A series of tests were made to determine the quantitative changes 

 in bacterial suspensions held in dilution water. From suspensions 

 held for two hours at room temperature triplicate plates on lactose agar 

 were made at fifteen minute intervals. 



Of fourteen tests made with dilutions of one part milk in one hun- 

 dred thousand parts water, five showed decreases ranging from ten to 

 seventy per cent in two hours, seven showed no definite change, and 

 two gave increases of thirty-two and thirty-nine per cent. 



Since colonies of the lactic acid type seemed to be the ones disappearing 

 thirty-two tests were made with milk inoculated with these organisms 

 in dilution water from five different sources. The same dilution 

 was used as before. Thirty of these tests gave unmistakable reductions 

 in numbers, amounting in some cases to fifty per cent in fifteen minutes. 



Additional tests of dilutions below one to one thousand made with 

 milk containing a mixed flora did not show any decrease during two 

 hours, but an increase was observed on longer standing. 



The nature of the organisms present and the amount of material 

 added to the dilution water from the original bacterial medium are 

 probable factors determining the effect of dilution water on the bacteria 

 present. 



Variation in Plate Counts Under Research Conditions. M. J. Prucha. 



Results of seven experiments are presented in this preliminary report. 

 In each experiment about one hundred lactose agar plates were pre- 

 pared using the same dilution of milk. 



Further study is needed to give sufficient basis for drawing definite 

 conclusions, but the results so far point to the conclusion that the 

 average of three plates from the same dilution approaches reasonably 

 closely to the average of a hundred plates made from the same dilution, 

 when that average is between one and two hundred colonies per plate. 



Another Use of the Double-Plate Method. W. D. Frost and Freda M. 



Bt^chmann. 



This method was used by Frost in 1904 to study antagonism among 

 bacteria. It was slightly modified, renamed and used by Churchman 

 in 1912 to study the bactericidal action of aniline dyes. 



It is here modified to obviate the necessity of using either a glass or 

 metal division by putting in a petri dish, before sterilization, a semi- 

 disc of cheesecloth. The bottom of the dish is entirely flooded with the 

 medium to be used and when hard the piece of cloth with the adherent 

 agar is lifted out with sterile forceps. The clear portion of the dish 

 is flooded with the medium containing the material to be studied. 

 Streaks of the organism to be used are then made over each side of the 



