FROST’S MICROSCOPIC PLATE METHOD 401 
the standard method to be employed. For the purpose of rapidly 
dividing raw milk into a series of grades, in such a way that the results 
can be obtained in the quickest possible time, the direct microscopic 
method seems to be extremely useful, and the results which are obtained 
will, in nearly all cases, agree with those obtained by the plate count, 
and probably in all cases will give a closer approximation to the fair 
grading than the plate count can do. For these reasons the use of the 
direct microscopic method is extremely valuable at the dairy end of the 
milk route, where the farmer wishes to know the kind of milk he is pro- 
ducing, or the purchaser at the shipping station wishes to know the kind 
that he is receiving from the farmer. It is of less value at the city end 
of the milk route, especially if pasteurization of the milk has been intro- 
duced anywhere along the route. It is especially useful in the data it 
gives concerning the kinds of bacteria present in milk, since it sometimes 
enables the farmer quickly to pick out from his herds such cows as are 
discharging large numbers of streptococci, thus giving a very efficient 
means of protecting the milk supply from this type of organisms that 
are to-day recognized as suspicious and decidedly undesirable. 
Goodrich (1914) finds a marked correlation between the microscopic 
and plate counts. He regards the factor of 20,000 which is used to 
reduce the microscopic count to terms of the plate count as satisfactory. 
Breed and Brew (1917) claim that their microscopic method is as satis- 
factory for controlling city milk supplies as is the agar plate method. 
Breed and Stocking (1917) found that the plate counts are characterized 
by greater regularity in the hands of laboratory assistants carrying out 
routine analyses of milk, than the microscopic method of Breed and 
Brew. Inexperienced workers are said to secure great errors in the use 
of the microscopic method. About the same conclusion was reached by 
Conn (1915). He stated that considerable experience was needed by 
the analyst to distinguish between bacteria and dirt particles. 
The Breed method has been demonstrated by the work of different 
investigators to be fairly accurate with milks which have large numbers 
of bacteria. It may scarcely be conceded that where the bacteria are 
so few that many of the fields of a Breed smear contain no bacteria, the 
count is very accurate. In this connection the Frost microscopic plate 
method or Allen’s microscopic method may be found to be more satis- 
factory. Brew has mentioned this last fact as a disadvantage of the 
microscopic method. To secure the greatest possible accuracy a large 
number of fields should be counted. 
Frost’s Microscopic Plate Method. This differs from the Breed 
Method of securing a microscopic count in that little plates are made 
