3O2 PRACTICAL DAIRY BACTERIOLOGY 



*No. 48. 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. 



*No. 49. 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 coeled. 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 com- 

 pare 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 temperature of an ordinary room and compare the 

 time of souring and curdling in the two cases. 



No. 50. The Effect of Careful Milking. Compare the effect 

 of milking, for six successive days, with and without precau- 

 tions. The first three days use open milk pails and make no 

 special attempt at cleanliness. The second three days use closed 

 milk pails, groom the cows, wash the udders and perform the 

 milking out-of-doors instead of in the closed barn. In each 

 case make a quantitative analysis of the number of bacteria in 

 the milk and compare the results. 



*No. 51. Sterilization by Boiling. Make a set of bacterial 

 plates from a sample of milk in gelatin. Then boil the milk for 

 five minutes in a flask closed with cotton and make another set 

 of plates, diluting by 10. Allow the boiled milk to stand for 24 

 hours and make another set of bacterial plates, diluting by 100. 

 Allow the rest of the boiled milk to stand in the laboratory until 

 it shows signs of fermentation. Determine whether it has 



