A YEAR IN -SCIENCE 101 



warm place. Make daily observations and 'record 

 results. What is the effect of heat on bacteria? Of 

 cold? 



C. Prepare two test tubes as follows : Boil two 

 test tubes in water and fill each half full of boiled 

 milk. Into one tube introduce some of the scum from 

 the tube of hay infusion. Close the tube with absorbent 

 cotton and set in a warm place. 



Take some scum from the hay infusion and mix it 

 with a teaspoonful of a 2% solution of corrosive sub- 

 limate, or of formalin, and let it stand ten minutes. 

 Then pour this mixture into the second tube. Close 

 with absorbent cotton and place beside the first tube 

 in a warm place. After a day examine the contents of 

 the two tubes. Is the milk still fresh in either tube? 

 How do you account for the condition found? 



From this experiment what conditions are favorable 

 to bacterial growth? What conditions are unfavor- 

 able? What are some of the methods of killing 

 bacteria? 



Exercise 68. Root tubercles. 

 Object: To show a use of bacteria. 



Apparatus 



Compound microscope Roots of legumes 



Slides, etc. 



Directions: Bring to the laboratory the roots of 

 any leguminous plants (pea, bean, vetch, etc.) Exam- 

 ine the roots carefully for nodules. Sketch to show 



