EXAMINATION OF WATER, AIR, AND MILK 121 



the milk when the tubes are immersed in it. Raise the 

 temperature to 75°, and keep it there by regulating the 

 flame. The tubes of milk are then immersed in the 

 water, and kept there for 30 minutes, as it requires about 

 10 minutes for the milk in the tubes to reach the tempera- 

 ture of the water. The tubes are then taken out and 

 cooled quickly by standing them in cold water. Place 

 one of the tubes at incubator and the other at room 

 temperature. Aerate the other two by shaking vigor- 

 ously for I J minutes. Keep one of these at room tem- 

 perature, the other in the thermostat. 



4. Place two more milk-tubes in the Arnold at 100° 

 for 30 minutes. Keep one at room temperature and one 

 in the thermostat. 



5. The remaining two tubes autoclav at 120° for 

 S minutes, and place one in the thermostat and keep the 

 other at room temperature. 



6. Note the conditions of these ten tubes after 2 or 

 3 days. Compare the results, and tabulate them. Note 

 especially coagulation, time elapsed before coagulation 

 sets in, gas-formation, condition of whey, film, and odor. 

 How are these differences explained? 



Plates in lactose-litmus-gelatin should be made from 

 each of these tubes, and the colonies studied and counted. 

 Subcultures on agar-slants may also be made, and the 

 usual media inoculated from these, if the individual 

 species are to be studied. 



