368 Animal Husbandry 
32. Stupy or THE KEEPING QuALITY oF MILK 
Object. To show the effect of temperature on the keeping 
quality of milk. 
Materials. Some fresh milk, sterile test tubes plugged. with 
cotton or some small glass jars or bottles, and a thermometer. 
_ Directions. Sterilize six jars or bottles by thoroughly scalding 
them in boiling water. Thoroughly mix the milk and put about 
equal amounts in each test tube or jar. Hold one at each of the 
following temperatures: 45°, 50°, 55°, 60°, 70°, 80° for several 
hours. This can be done by putting the test tubes or jars in dishes 
of water and using ice for holding the lower temperatures and hot 
water for the higher ones. The different temperatures should be 
maintained for from five to eight hours. At the end of this period, 
place all the jars at the same temperature and note the time when 
each curdles. It is well to get the milk from several sources and 
run different series of samples. If the samples are held at the 
different temperatures during the day, and placed together at the 
close of school, some may curdle during the following night, but 
most of them will curdle during the next day, and enough data can 
be obtained to show a difference in the keeping quality. 
33.. PASTEURIZATION OF MILK 
Qbject. To show the effect of heating upon the keeping qual- 
ity of milk. 
Materials. Some fresh milk from a clean stable and some from 
a dirty stable and some clean test tubes with cotton plugs. 
Directions. Fillseven test tubes from each sort of milk to a depth 
of 13 to 2 inches. Place one of each at room temperature. Heat 
a dish of water to 145°F. Place the remaining tubes of milk in 
the water, and remove as follows :— 
One of each kind of milk at the end of 1 minute 
One of each kind of milk at the end of 2 minutes 
One of each kind of milk at the end of 3 minutes 
