APPENDIX 313 



63. Washing of Milk Vessels. Place some ordinary milk in two 

 test tubes and set aside until the milk sours. Pour out the milk from 

 all the test tubes and wash one with cold water and the other with hot 

 water and soap. Hold the tubes up to the light and notice the dif- 

 ference in the cleanliness of the two test tubes. Now fill each tube 

 with fresh milk and set aside in a moderately cool place and notice in 

 which of the tubes the milk sours first. 



63. Vinegar Bacteria. Obtain a little good vinegar containing 

 some of the mother of vinegar. Put a bit of the mother upon a glass 

 slide, cover with a cover glass to spread in a thin layer, and study 

 with a high-power microscope. 



64. Effect of Heat in sterilizing Fruit. Fill four test tubes about 

 half full of water. In each place a few small berries, like blackber- 

 ries or blueberries, or pieces of cherry, apple, or pear. Plug each 

 tightly with cotton. Put one aside and label a. Place the others 

 in cold water and gradually bring the water to a boil. Before the 

 water boils take out one test tube and label it b ; take out a second 

 the moment the water boils and label c; remove a third after the 

 water has boiled half an hour and label d. Set all tubes aside in a 

 warm place and watch for several days, determining which are suc- 

 cessfully sterilized, which will be indicated by their not spoiling. 



