EXERCISE 43 (Continued) 



the sterilizer boiling for twenty minutes. Allow the tubes to cool, repeat the treatment twenty-four 

 hours later, and preferably a third time one day later. If no sterilizer is to be had, set the tubes in 

 a vessel of water in such position that they are half immersed in the water but are not in contact 

 with the bottom of the vessel. Boil as directed above. 



It is supposed that the heating will have killed any living things in the tubes, as in Exercise 42. 

 The three sterilizations are intended to make sure of this. Set aside one of the sterilized tubes to see 

 whether any changes will occur in it. Label it " 2." Do not at any time during the experiment 

 remove the cotton plug. Label the remaining tubes " 3," " 4," " 5," " 6." 



When tubes " 3 " to " 6 " have cooled from the last sterilization, treat them as indicated in the 

 tabulation above. Keep a daily record of observations for at least a week. Curdling, becoming 

 watery, and alterations of color are changes which are easily seen. 



Make each tube the basis of a statement regarding what you have learned from it. Your notes 

 should include, in addition to the statement of the method of preparing and sterilizing the tubes and 

 a statement of the conclusions, a tabular presentation of the records of the experiments. 



Additional problems. Is there objection to the use of formalin in preserving milk ? 



Why is absolute cleanliness necessary in handling milk ? How can such cleanliness be secured ? 



What is the importance to the public of having great care observed in handling milk ? 



When canning fruit, should the fruit be allowed to cool before the lids are placed on the cans ? Why ? 



[56] 



