The Effect of Distilled Water upon the Tendency to Colony Formation upon Petri Plates

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Abstract
The macroscopic colony count has been used for many years as a measure of the bacterial population of milk. In the numer- ous laboratories throughout the country it is considered the stand° ard method, supported as it is, by the American Public Health Association. The first edition of Standard Methods mentioned only the plate method, which seemed to be adequate for the t~inds of milir produced at that time. The numbers of bacteria found in milk were high as a rule, and one had but to separate the bad from the worse. In the four subsequent editions of Standard Methods other methods have claimed attention and obtained supporters, somewhat to the detriment of the plate method. Paralleling this diversity of methods there likewise has been an improvement in the milk itself, for there is no longer the large spread between mille d high and low qll~llty. Such conditions place a greater tax upon the method which was devised primarily to eliminate the poorest milk. There is small wonder then that the plate method has seemed to be less accurate. Too much is expected of it today. It is not an instrument of precision, which fact is recognized by the revis- ing committees, as is evidenced by the statement in the introduc- tion to the various editions of Standard Methods. Furthermore, it has recently been shown that Standard Methods have not had a fair chance. The Report of the Referee for the Bacteriological Exsmlnation of Milk (1) indicates that many brands of peptone and beef extract are used in amounts varying as much as 100 per cent from those considered standard. The reaction of the me- dium, the time and temperature of incubation were frequently quite di~erent from those permitted. Now the methods have

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