130 INTERRELATIONS OF PLANTS AND ANIMALS 



has been sterilized). Set it in a vessel of boiling water just 

 removed from the flame, and heat it to 150-160 F. or 66-72 

 C., stirring with a clean spoon for 10 minutes. Let it remain 

 for 15 minutes, then quickly cool. Set it aside with the other 



jar, and compare them 

 after a day or so. Re- 

 sult ? Taste, odor, 

 etc.? Which is the 

 sweeter tasting? 

 Which has the sweeter 

 odor ? Which is there- 

 fore purer, or freer of 

 germs ? 



Note. Discontinu- 

 ous sterilization or pas- 

 teurization may be per- 

 formed by heating the 



FIG. 37. Pasteurizing apparatus. 



substance to be sterilized twice a day just as for ordinary ster- 

 ilization. Continue thus for two or three days. Why ? 

 Conclusions. 1. How may milk be pasteurized ? 



2. What is the benefit of pasteurization ? 



3. Why should milk be marketed in bottles ? 

 Observations. 1. Carefully pour the milk from the pail or 



bottle at home, after it has stood several hours, and see if there 

 is any sediment left. Result ? 



2. Taste the milk used at home. Does it leave a slightly 

 unpleasant taste, reminding one of the odor about cow 

 barns ? If so, the milk should be pasteurized before using. 



Note. Boiling may do, but it renders it somewhat more difficult of 

 digestion and also changes the taste, so that it is especially distasteful to 

 some ; therefore pasteurization is to be preferred. 



Conclusions. 1. What do you think the sediment in milk 

 is likely to be ? 



2. Would there likely be bacteria in the filth in which 

 cows*Tiave been lying ? 



Observations. 1. Rinse out a recently emptied milk bottle 



