Quantitative Bacteriological Examination. 43 



exceed 200, for when the number is very high the colonies 

 grow only to a small size, making counting laborious and 

 inaccurate, and many do not develop at all. The best 

 results are obtained with numbers ranging from 50 

 to 200. 



EFFECT OF THE LENGTH OF INCUBATION OF WATER 

 BACTERIA IN GELATIN UPON THE NUMBER OF COLO- 

 NIES DEVELOPING. 



(MIQUEL AND CAMBIER, 1902.) 



When it is possible to do so, all the colonies on the plate 

 should be counted. When they exceed 400 or 500 it is 

 often easier, and fully as accurate, to count a fractional 

 part of the plate and estimate the total number therefrom. 

 This should not be done, however, except in case of 

 necessity. 



It is customary in determining numbers to make plates 

 in duplicate, thereby affording a check upon one's own 

 work. Owing to the lack of precision in the method, the 

 limit of experimental error is a wide one. It should be 



