294 MILK 



tests that were made with this apparatus consisted in enumerating 

 the number of bacteria in the air by use of a specially designed 

 aeroscope. Sterile water was "milked" from the udder into a 

 narrow-top pail for the same length of time as was required to 

 aspirate 7 liters of air through the aeroscope. As a check some 

 of the sterile water from the "tin udder" was "milked" into sterile 

 test-tubes. Another parallel test consisted in placing 500 to 

 1000 c.c. of sterilized tap-water in a pail having an opening of 

 266 sq. cm. This pail was kept covered until the other tests were 

 commenced. The cover was then removed and not replaced be- 

 fore the other tests were finished. Pails were also placed on the 

 floor beside the apparatus to receive dust dropping from the air. 

 The results of these exhaustive tests were these: During such 

 barn operations as milking, feeding hay, grain, and the like the 

 number of bacteria per liter of air would run from 50 to 200. 

 The extremes were much lower and up to 825 per liter. When 

 sterile water was "milked" from the "tin udder" the germ content 

 of the "milked" water averaged 12 bacteria per cubic centimeter, 

 with a maximum of 73. In similar tests made in the stable loft, 

 where dust was raised by sweeping the floor, the air contained 

 1000 to 2000 bacteria per liter, with a minimum of 329 and a 

 maximum of 5200. When the dust was raised continuously 

 throughout the test period the average was 2500 to 10,000 bacteria 

 per liter. 



Sterile water "milked" under extremely dusty conditions aver- 

 aged 47.6 bacteria per cubic centimeter, and when the dust was 

 maintained throughout the test period it averaged 604. The 

 authors further enumerated the number of bacteria that would 

 develop from the dust dropping into milk contained in an open 

 12-inch pail during one hour. The maximum was 199 bacteria 

 per cubic centimeter. 



The conclusion drawn by the authors from these experiments 

 is that "occasionally under exceptionally dusty conditions the 

 number of bacteria getting into the milk from the air may be ap- 

 proximately as high as the number derived from the udder, but 

 the number so derived under ordinary conditions does not increase 

 the germ content of the milk to any important extent." 



The work published by Ruehle and Kulp is a great aid in the 

 study of sources of the bacterial content of milk, but it should 

 not be interpreted as an encouragement to uncleanliness of barns. 

 On the contrary, as it shows exactly how the germ content of 

 milk is increased from dust in the air, it also shows by how 

 much the germ content can be kept down by avoiding dust- 

 raising operations immediately before or during the process of 

 milking. 



