62 EXPERIMENTAL DAIRY BACTERIOLOGY 



and hung in a damp milk room or creamery will soon be a 

 source of contamination. 



The number of bacteria to be found in any utensil is de- 

 pendent not only on the manner of washing, but on whether 

 or not it has been thoroughly dried. If small amounts of 

 water are left in cans, pails, bottles, etc., a profuse growth of 

 bacteria will take place, for the water will contain sufficient 

 organic matter for food, no matter how carefully the utensil 

 was cleaned. 



The bacteriological condition of any utensil can be deter- 

 mined by rinsing it with sterile water and preparing quanti- 

 tative plates from the water. The walls and bottoms of pails, 

 cans, etc., should be scrubbed with a sterile brush, especial 

 attention being given to the seams. Cloth strainers may be 

 rinsed in sterile water and this examined. Milking machines 

 should have a considerable volume of water passed through 

 the teat cups and rubber tubes into the can. Separators are 

 examined in a similar way. 



Exercise. Each student will test the bacteriological condition of 

 pails, strainers, and farm separators, which have been treated in the 

 various ways generally employed in farm and creamery practice. 



PAILS AND CANS. Sterilize two flasks of water containing 100 cc. 

 each. Place two test-tube brushes in large test tubes, stopper with 

 cotton, and sterilize with the flask of water. Pour a flask of the 

 sterile water into the utensil to be examined, scrub the walls and 

 bottom, and especially the seams with the test-tube brush. Return 

 the water to the flask and from it prepare quantitative lactose-agar 

 plates. From the data obtained, calculate the number of bacteria that 

 would have been added to the milk in case the vessel used had been 

 filled with milk. 



CLOTH STRAINERS. Sterilize a liter of water in a small pail or 

 can. Rinse a strainer in this water as well as possible, wringing out 

 the cloth. Examine the water quantitatively. 



FARM SEPARATORS. A quantity of milk should be passed through 

 the separator and the milk removed by flushing the machine with a 

 couple of gallons of cold water. 



