Working with 100 weigh-can samples from 5 dairies it was found that icing for even 2 hours slightly retarded reduction of methylene blue; after 23 hours the effect was somewhat greater when the dye was present, but not when it was added just before incubation. With resazurin, on the other hand, there was better agreement when the dye was present during overnight storage. In no instance was the difference statistically significant. Methylene blue reduction times were in surprisingly close agreement with standard plate counts on the raw milk, while the correlation between reduction times (raw) and plate counts after laboratory pasteurization was better than was expected.

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Author notes

Dr. C. K. Johns is Senior Bacteriologist with the Division of Bacteriology and Dairy Research, Canada Department of Agriculture, Ottawa, Ontario, where he has been since 1927. A graduate of the University of Alberta, he obtained his M. Sc. from McGill University and his Ph. D. from Wisconsin. He was President of the I.A.M.F.S. in 1934–35, and is a Fellow of the American Public Health Association, where he serves as a Referee for the Subcommittee on Standard Methods for the Examination of Dairy Products.