EXPIERIMENT STATION REPORTS. 185 



Comparing the tests and retests on all of the samples of milk in Groups 

 II and III using both the pH method and counts in various media, the 

 sensitiveness of the methods appears as follows : 



pH score 91.0% efficient 



Bacto Agar G6.6% efficient 



Meat infusion agar G6.6% efficient 



Milk powder agar A 63.3% efficient 



Beef extract agar 60.6% efficient 



Greater sensitiveness of methods would be expected if the samples 

 have a liigh initial bacterial count. Methods which show poorer condi- 

 tion ui)()n retest of samples with low initial counts should be the most 

 vahiable. 



If only those samples of milk having a retest average count of under 

 25,000 bacteria per cubic centimeter are considered the efficiency of the 

 various methods and media is as follows: 



pH score 84 . 6% efficient 



Bacto agar 61.5% efficient 



Infusion agar 30.0% efficient 



Agar A 30. 0% efficient 



Extract agar 23 . 0% efficient 



Considering only those samples having a retest average count be- 

 tween tweiity-tive thousand and 100,000 the results are as follows: 



pH score 85 . 7% efficient 



Infusion agar 85.7% efficient 



Agar A 85 . 7% efficient 



Extract agar 71.4% efficient 



Bacto agar 28.5% efficient 



The samples of milk having retest counts between 100,000 and 1,000,- 

 000 bacteria per cubic centimeter give the following results: 



pH score ■ 100% efficient 



Infusion agar 100% efficient 



Bacto agar 80% efficient 



Extract agar 80% efficient 



Milk powder agar 60% efficient 



Kamides of milk with retest counts of over 1,000,000 give results as 

 follows : 



pH score 100% efficient 



Bacto agar 100% efficient 



Extract agar 100% efficient 



Agar A 100% efficient 



"^f-i 



Infusion agar 87.5% efficient 



The pH score of the samples of milk after incubation was at times 

 the same as before but it never indicated that the milk was in better 

 condition after the samples had been siibjected to the short incubation 



