LABORATORY EXEHCISES. 



Examine the three bottles of milk at the end 

 of. 12 hours. 



1. Do you notice any difference in the smell or 



taste of No. i, No. 2, and No. 3? 



2. Boil the milk in bottle No. 3 again; clean 



the bottle and cork in boiling water as 

 before, and replace the milk in the bottle ; 

 cork the bottle. Put bottle No. i back 

 in the ice-box ; return bottles No. 2 and 

 No. 3 to the place from which you took 

 them. 



3. Examine all three bottles at the end of a 



second 12 hours. Have any further 

 changes taken place? 



4. Carry out the directions given in 2 above a 



second time. Repeat your examina- 

 tions at the end of each successive 12 

 hours for two or three days, each time 

 boiling the milk in bottle No. 3. Record 

 in your note-book each time the changes 

 which you observe in each of the bottles. 



5. The changes in the milk are caused by the 



growth of bacteria from the air or on the 

 bottles or stoppers. 



a. What effect does a cold temperature 



have on the growth of bacteria? 



b. What effect does boiling have on the 



growth of these cells. 



c. What is the most favorable tempe^a- 



ture for the growth of bacteria? 



d. What effect do some bacteria have on 



the milk? 



