COLONIES ALLOWABLE ON AGAR PLATES 



325 



The results given in the lower part of table 1 were calculated 

 from the same counts, the groups of plates having been arranged 

 differently. From this part of the table it will be seen that 

 the percentage of discrepant plates is practically the same 

 for the groups of plates having 20 to 400, 30 to 400, 20 to 200, 

 30 to 200, or 40 to 200 colonies per plate, the best showing being 

 made by the group of plates having more than 40 and less than 



TABLE 1 



Plate counts after incubation at 21 ° C. arranged to show the number and percent- 

 age of counts in groups according to (he number of colonies per plate 



Total number of counts summarized in this table 1435. 



200 colonies per plate. Plates having less than 30 colonies or 

 more than 400 colonies show very large percentages of dis- 

 crepancies. 



Table 2 gives the results obtained by counting 1056 of the 

 same plates as those whose counts are summarized in table 1 

 after two days of additional incubation at 37°C. In general 

 the results obtained from these counts are similar to those given 

 in table 1. However the best showings are made in this case 

 by groups of plates having more than 200 and less than 400 colo- 



