VARIATIONS IN BACTERIA CoUNTS 225 
poured with standard plain agar; nine with nutrient agar containing 1 
per cent of dextrose; and nine with nutrient agar containing 1 per cent of 
lactose. The different agars were all made from single, large-quantity 
batches of plain, nutrient agar. These were subdivided, and the definite 
percentage of the particular carbohydrate desired was added to each. 
Three of the nine plates containing the different agars were incubated at 
37° C. for forty-eight hours; three at 30° C. for five days; and three at 
20° C. for five days. With the exceptions noted, the technique given in 
the Standard Methods was carefully followed. It was necessary, however, 
to include counts from plates containing fewer than 30 colonies and 
more than 200 colonies, altho in all cases the dilution was designed to give 
colonies between these limits from the forty-eight hour count at 37°. 
In table i are shown the counts obtained from 100 different samples of 
milk from each of the nine combinations of incubation temperatures 
and media. The individual counts appearing in this table are the averages 
of triplicate plates. Each plate of the series of three checked with the 
other plates of the series as closely as would be expected from duplicate 
or triplicate plates from the same dilution of any sample of normal milk. 
In order to indicate in a comprehensive manner the variations obtained, 
the 37° count was taken as the standard. Any variation above or below 
this count 1s indicated by a plus or a minus sign. The variations are 
shown also as. percentages, the 37° count being accepted as 100 per cent, 
and counts higher or lower being indicated by figures above or below 100. 
