96 LABORATORY EXERCISES. 



temperature of the room and 

 record result. 



(3) (Yeast is a plant.) Has it been 

 killed by the cold? Give 

 reason for your answer. 



b. Pour some more of the working yeast 



mixture into a tin cup, place it on 

 the stove and boil it. Allow the 

 mixture to cool to the tempera- 

 ture of the room, and turn it into 

 a small bottle. 



(1) What effect does boiling have 



on the activity of the yeast ? 



(2) Keep the mixture for a day or 



two. Was the yeast killed 

 by the heat? 



c. Summary. 



(1) What temperature do you find 



to be most favorable for the 

 growth of yeast? 



(2) What is the effect of extreme 

 . cold? 



(3) What is the effect of a high de- 



gree of heat ? 



9. (Dem.) Nearly fill a bottle with a yeast 

 mixture which is working well. Insert 

 a rubber cork in the mouth of the bottle 

 through which passes one arm of a U- 

 tube. Half-fill a test-tube with lime- 

 water. Allow the free end of the U-tube 

 to dip below the surface of the lime- 

 water. Be sure all the connections are 



