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ROBERT S. BREED AND W. D. DOTTERRER 



nies per plate (87 per cent of satisfactory plates), the group 

 of plates having 100 to 200 colonies (82.4 per cent) and the 

 group having 30 to 400 colonies per plate (81.4 per cent). As 

 in table 1 there is a marked increase in the number of discrepant 

 counts from plates having less than 30 or more than 400 colonies 

 per plate While the results in table 1 favor the 40 to 200 

 group rather than the 30 to 400 group by 2.9 per cent., the same 



TABLE 2 



Plate counts after two additional days of incubation at 37° C. arranged to show the 

 number and percentage of counts in groups according lo the number of colonies 

 per plate 



Total number of counts summarized in this table 1056. 



comparison in table 2 shows an advantage of 1.6 per cent for 

 the 30 to 400 group This indicates that there is little advantage 

 in selecting one group of plates in preference to the other. 



In the fourth and fifth columns of these two tables, the num- 

 ber of cases is shown in which the discrepancy was caused by 

 having too few or too many colonies on the plate Arranging 

 the plates in the groups to 10, 10 to 20, 20 to 30, 30 to 50, 50 

 to 100, 100 to 200, 200 to 400 and more than 400 colonies per 



