1902-3.] Bacterial Contamination of Milk. 467 



THE BACTERIAL CONTAMINATION OF MILK AND ITS 



CONTROL. 



By F. C. Harrison, Professor of Bacteriology, Ontario 

 Agricultural College, 



{Read 28th February, igoj.) 



Milk as sold in cities, towns or villages contains a varying number 

 of bacteria according to its age, the amount of sediment in it, and the 

 temperature at which it has been kept. Soxhlet,^ Uhl,^ Backhaus^ and 

 others have shown that the more dirt or sediment, the more bacteria 

 there will be, and Renk* has given us some interesting experimental data 

 on the amount and kind of filth present in ordinary market milk. This 

 filth is largely made up of excrementitious matter, vegetable fibres, 

 epithelial debris, hairs of the cow, dust particles, etc., and the amount of 

 filth contained in a litre of milk furnishes a positive index of the degree 

 of cleanliness observed in the dairy stable. Renk found the following 

 amount of dried impurities in the milk supply of the following German 

 cities: Leipzig, 3.8 milligrams; Munich, 9 milligrams; Berlin, 10.3 

 milligrams; Halle, 12.2 milligrams per litre; and Hird^ found in the 

 Washington, D.C., milk supply, 5.30 milligrams of filth per quart. 



Backhaus^ has also shown that 50 per cent, of fresh manure dissolves 

 in milk and does not appear as sediment ; and therefore the weight of 

 undried filth in all these samples would have been more than doubled. 

 This investigator has also determined by actual tests that the daily milk 

 supply of Berlin, Germany, contains about 300 pounds of dirt and filth. 

 Further, many of the bacteria derived from such sources are very harm- 

 ful, for not only are such fecal bacteria concerned in the intestinal 

 troubles of infants, but they also give rise to abnormal fermentations in 

 butter and cheese, producing taints, off-flavours, and decomposition 

 products in these foods. 



For the guidance of the dairyman who buys milk for sale, and for 

 the housewife, Renk* suggests the following rule: If a sample of milk 

 shows any evidence of impurity settling on a transparent bottom within 

 two hours, it is to be regarded as containing too much solid impurities. 



When we examine the results relative to the number of bacteria in 

 European market milk, we are at once struck by the enormous numbers 

 that are frequently present. 



