136 PHYSIOLOGY FOR THE LABORATORY. 



3. The color of the colonies. What colors do you 

 find? 



b. Ice may be examined by melting it and examining 

 the water obtained, as in a. 



1. Should ice be placed directly in drinking water ? 



Why not? 



2. How may drinking water be cooled? 



II. BACTERIA IN MILK. 



Materials. 3 c.c. of fresh milk. 10 c.c. of nutrient gelatin. 

 Apparatus. A sterilized Petri dish. 



Pour the milk and then the warm nutrient gelatin into 

 a Petri dish. Mix the water and gelatin and label the 

 culture. Keep in a warm, dark place and watch from day 

 to day for the appearance of the colonies. Compare these 

 colonies with those obtained from the examination of 

 drinking water. Study these in the same way. 



III. BACTERIA IN DUST. 



Materials. A little dust gathered from the floor, the top of the 

 door, or back of a picture. 10 c.c. of nutrient gelatin. 



Apparatus. A sterilized Petri dish. A compound microscope. 



a. Pour the warm nutrient gelatin into the dish and 

 scatter a little dust over it. Place in a warm room and 

 watch for the appearance of the colonies. Compare these 

 with the colonies obtained from the examination of water 

 and milk. 



b. Mount a little dust in water on a glass slide and 

 examine with the compound microscope. What do you 

 find? 



