306 CLEAN MILK 



machine in motion and rotate rapidly for ten minutes. By this time 

 the sediment will mostly be thrown to the smaller end of the tube. 

 The cream and milk are then to be carefully removed from the sedi- 

 ment with a pipette, and the tube filled up again with clean water 

 and centrifugalized again. This is to be repeated until the water be- 

 comes clear, after which the sediment in the bottom of the tubes 

 is to be carefully washed out with clean water upon a filter, and 

 the rest of the procedure is as above. 



c. Third method. Procure some bolting cloth of the finest 

 mesh. The meshes should be fine enough to retain all the visible 

 particles, but to allow fat particles to pass through. Place in a 

 ribbed funnel, moisten with water, and pour through it cne quart 

 (or liter) of milk. Wash the material left on the cloth with water 

 and then with a mixture of ether and alcohol, equal parts. Wash 

 the dirt on to a carefully weighed filter paper. Dry thoroughly and 

 weigh as above. 



28. The Covered Milk Pail. — Milk two cows, one into 

 an ordinary milk pail with a flaring, open mouth and the other into 

 a covered milk pail. Determine the amount of dirt in the milk in 

 each case. Immediately after the milking, in each case, make a 

 quantitative count of the number of bacteria, comparing the results 

 together, and determine the value of a covered milk pail. The next 

 day repeat the experiment, reversing^the two cows. 



29. Advantage of Immediate Cooling. — Immediately after 

 milking, cool, by aerating, part of the milk, and place in steril- 

 ized jar. Fill another similar jar with milk not cooled. Fill a third 

 jar with milk cooled by immersing at once in iced water. Place all 

 three jars side by side in an ordinary room and compare the time 

 of souring and curdling in the three specimens. 



Cool night's milk immediately, as cool as possible. The next 

 morning fill two jars, one with the night's milk that has been cooled 

 and the other with the milk warm from the cow. Place both at a 



