MILK-POWDER AGAR FOR THE DETERMINATION OF 

 BACTERIA IN MILK 



S. HENRY AYERS and COURTLAND S. MUDGE 



From the Research Laboratories of the Dairy Division, United States Department 



of Agriculture 



Received for publication May 27, 1920 



Before presenting descriptions of new media for the deter- 

 mination of bacteria in milk, we wish to call attention to the 

 fact that the media described give not only quantitative but, 

 to a certain extent, qualitative results. If the new media 

 achieved merely the same results as those now well known, we 

 should not feel warranted in taking up the reader's time. 



It is believed that the time has passed when one can be satisfied 

 with total counts only. Mere quantitative results in bacterio- 

 logical milk analysis can not be interpreted satisfactorily unless 

 something of the history of the milk is known. Often this 

 "something" is missing; then one must interpret the count as 

 due to this, that, or the other condition or a combination of them. 

 This is not an attempt to discredit the total bacterial count, 

 for it is very valuable as it stands, in milk-control work, but it 

 is hoped that some of the media described in this paper will 

 increase its value. 



The media extensively used in milk-control work have been 

 (1) infusion agar, described in the standard methods of the 

 American Public Health Association in 1910, and (2) extract 

 agar, later adopted as a standard medium, its formula having 

 been published by the association in 1916. 



Many who use the extract agar realize that it does not give 

 the high counts which are obtained on the infusion agar, but 

 use it because it is the standard medium for milk analysis. Even 

 the members of the Committee on Standard Methods recognized 

 the fact that extract agar is defective, as is shown by the state- 



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THE JOURNAL OF BACTERIOLOGY, VOL. V, NO. 6 



