Colonies for a Satisfactory Soil Plate. 99 
Table III has been compiled to show the ratios between the counts of 
the two dilutions when the number of colonies developing on the 1—40,000 
bacterial dilution is under 100. These results are the cases where the 
counts from twenty-four soil samples averaged under 100 cn the 1—40,000 
bacterial dilution. 
TABLE III. 
Colonies on 1-40,000 and 1-400,000 Bacterial Dilutions. 
(Counts on 1-40,000 Bacterial Dilutions between 47 and 100.) 
DILUTIONS 
1-40,000** 1-400,090 
| 
| 
94.5 12.0 
91.7 12.3 
88.0 1355 
88.0 11.0 
86.3 9.0* 
80.3 aoe 
74.0 8.0* 
65.3 8.0* 
65.0 Don 
56.0 Oe 
51.0 4.0* 
48.0 5.0* 
47.0 onoF 
Averageall 71.9 8.3 
Average * 63.6 6.6 
**Counts are averages of triplicate plates. 
*These numbers multiplied by 10 are within 15 of the numbers obtained in the lower bacterial 
dilution. 
Table III brings out that, while 100 colonies per plate are quite 
satisfactory, the 10 to 1 ratio is more nearly approximated when much 
less than 100 colonies were present per plate. 
To further substantiate the evidence that results are reliable when 
relatively small numbers of colonies are present per plate, the ten-day 
counts from the 1—40,000 and 1—400,000 bacterial dilutions of a sandy 
soil, low in organic matter, are given in Table IV. 
