STUDY OF BA'Jl'ERTA. , . 101 



Shake the mixture and put it in a warm 

 place, noting the temperature. 



a. What becomes of the hay? Why? 



b. What is the color and smell of the hay 



infusion ? 



2. Examine the mixture after each 24 hours 

 for a week. 



a. What has now become of the hay? 



Why? 



b. What change takes place in the color 



and smell of the liquid? (These 

 changes are caused by bacteria.) 



c. What do you see on the surface of the 



infusion? (This is composed of 

 countless numbers of bacteria.) 

 B. Growth of bacteria in milk (at home). 



Secure three clean bottles of about the same 

 size, two of them provided with stoppers. 



Into one of the bottles pour some good fresh 

 milk; cover and place in the ice-box, or in 

 some other cold place. Label the bottle " No. 

 i." 



Pour into the second bottle about the same 

 amount of milk, and set it aside in a moder- 

 ately warm place, leaving it uncorked. Note 

 the temperature by means of a thermometer. 

 Label "No. 2." 



Clean the third bottle and the cork in boiling 

 water. Boil some of the milk 5 minutes, and 

 pour it into the bottle while hot. Cork the 

 bottle and place it beside the second bottle. 

 Label "No. 3, Sterilized milk." 



