LAl'.OK. \TOKY WORK IN DAIRY BACTEKK >L< )( iV 30! 



hours. A deposit of dirt will collect at the bottom, which may 

 easily be seen, by looking through the glass. With a siphon 

 carefully remove the milk to within *4 inch of the bottom, but 

 do not disturb the sediment. Fill up with clean water and allow 

 to settle again. Once more, after settling, siphon off the liquid, 

 and fill the glass with water. Repeat this operation several 

 times, until the water becomes fairly clear. Then, after allow- 

 ing the material to settle again, siphon off a considerable portion 

 of the liquid, and after thoroughly mixing the sediment with 

 the remainder of the water in the cylinder, pour it through care- 

 fully weighed filter paper; wash the filtrate by means of water 

 through the filter paper. Remove the filter paper and dry, until 

 it comes to a constant weight. Weigh. The difference in weight 

 between this and the original weight of the filter paper will give 

 the weighed amount of dirt collected. 



b. Second method. Place a definite quantity of milk, usually 

 10 c.c., in one of the glass tubes of a centrifugal machine. Set 

 the 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 re- 

 moved from the sediment with a pipette, and the tube filled up 

 again with clean water and centrifugalized again. This is to 

 be repeated until the water becomes clear, after which the sedi- 

 ment 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 one 

 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. 



