100 LABOBATOBY MANUAL 



of colonies of bacteria. Describe and sketch the 

 appearance of the growths. What do these experi- 

 ments show as to the prevalence of bacteria ? 



Exercise 67. Conditions for Bacterial Growth. 

 Object: To determine conditions for bacterial 

 growth. 



Apparatus 



Hay . Test tubes 



Milk Absorbent cotton 



Meat 



Directions : A. Prepare three test tubes as follows : 

 Put in one some pieces of chopped hay and cover with 

 water; in the second some milk; and in the third a 

 small piece of meat covered with water. Set these 

 aside, uncovered, for a few days and note the changes 

 in appearance and odor of the contents. Mount some 

 of the scum on a slide and cover with a cover glass. 

 The instructor will find the bacteria for you under the 

 high power of the microscope. Determine the shape 

 of some of these bodies and sketch. 



B. Prepare three test tubes as follows: Fill each 

 tube half full with milk. Place one in a beaker and 

 pack ice around it. Leave the top open. Set the 

 entire apparatus on ice in the refrigerator. Boil the 

 contents of the second tube for a few minutes and 

 stopper with sterilized absorbent cotton. Set aside in 

 a warm place. Place the third tube, uncorked, in a 



