A RAPID METHOD

HAS BEEN DEVISED FOR

COUNTING BACTERIA IN MILK

BY

Prof. W. D. FROST, of the Bacteriology Laboratories of the Department of Agriculture, University of Wisconsin.

The two items illustrated here are the principal pieces of apparatus required.

Warming Table

DESCRIPTION OF TECHNIQUE:

For complete description of the methods and apparatus required, see the following: Journal of Infectious Diseases, Vol. XXVIII,

No. 2, February, 1921, pages 176-184, "Im-
proved Technique for the Micro or Little
Plate Method of Counting Bacteria in
Milk," by Dr. W. D. Frost.
Standard Methods for the Bacteriological
Examination of Milk, Third Edition, page
18, "Microscopic Colony Count (Frost
Method)," published by the American
Public Health Association.

ADVANTAGES OVER STANDARD PLATE METHOD

1. Rapidity of method, requiring only from 1/12 to 1/4 of the time required with the standard plate method.

2. Simplicity of technique.

3. Economy, due to small amount of materials required, both apparatus and media.

4.

Special adaptability for field work, because of the light and compact equipment. The carrying case may serve as an incubator.

5. Feasibility of determining total number of bacteria by making single cells visible through proper staining.

6. Possibility of identifying, by means of the higher powers of the microscope, the different organisms present through their individual peculiarities as shown on the little plate.

7. Ability to distinguish dead from living bacteria, in connection with the study of pasteurization.

8. Ability to keep a faithful permanent record for future use by filing the dry slides.

9. Reliability of the method, since the little plates can all be counted due to (1) the relatively large amount of milk used, (2) smaller dilution required and (3) lack of interference from spreaders.

ACCURACY

Numerous tests made by Frost and others show that the results secured by this method compare reasonably well with those obtained by the standard plate method. Variations between the two methods are no greater than between duplicate determinations by the standard plate method.

For Complete Descriptions and Directions for Use, send for Bulletin 97S.

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