INTERRELATIONS OF PLANTS AND ANIMALS 129 



once and set it in a warm place. Observe the results in three 

 days. Five days. 



7. Seal No. 7 and place it in an ice box or in cracked ice. 

 Observe the results in three days. Five days. 



8. Tabulate your results as follows : 



Conclusions. 1. Which of the above methods of disinfection 

 do you think is the best ? Why ? 



2. Why is it necessary to heat foods before canning them ? 



3. Why is hay dried before it is put into the barn ? 



4. Why put foods in the refrigerator in the summer time ? 



5. What conditions hinder the growth of bacteria ? 



2. PASTEURIZATION 



Note. Pasteurization is the heating of a substance to about 

 160 F. long enough to kill most of the germs. 



Materials. One pint of milk, two sterilized fruit or agate 

 jars, thermometer, alcohol lamp or Bunsen burner, double 

 cooker or hot air sterilizer. 



Note. Special pasteurization apparatus as shown in Figure 37 may 

 be procured for a small sum. 



Observations. 1. Put a half pint of milk in one of the 

 sterilized fruit jars, and set it uncovered in a warm place. 

 Result after two days ? Taste, odor, etc. ? 



2. Place a half pint of milk in another of the sterilized jars 

 (or it may be placed in the inner vessel of a double cooker that 

 SHARPE'S LAB. MAN. 9 



