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. 



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 Exam- 

 ination of Milk, Third Edition, page 18, 

 "Microscopic Colony Count (Frost 

 Method)," published bj^ the American 

 Public Health Association. 



ADVANTAGES OVER STANDARD PLATE METHOD 



Rapiditj' of method, requiring only from 1/12 to 1/4 of the time required with the stand- 

 ard plate method. 



Simplicity of technique. 



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



Special adaptability for field work, because of the light and compact equipment. The 

 carrying case may serve as an incubator. 



Feasibility of determining total number of bacteria by making single cells visible 

 through proper staining. 



Possibility of identifying, by means of the higher powers of the microscope, the differ- 

 ent organisms present through their individual peculiarities as shown on the little plate. 



Ability to distinguish dead from living bacteria, in connection with the study of pas- 

 teurization. 



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



Reliability of the method, since the little plates can all be counted due to (1) the rela- 

 tively large amount of milk used, (2) smaller dilution required and (3) lack of inter- 

 ference from spreaders. . 



Warming Table 



9. 



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 deter- 

 minations by the standard plate method. 



Moist Chamber Cabinet 

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





U^yTA. 



