TYPES ^OF MICROORGANISMS IN SOIL 243 



partially fill a small sterile flask with swamp or marsh water. 

 Examine immediately in the hanging drop and draw the 

 forms seen. 



12. Place this swamp water in the sunlight (more or 

 less direct) for two or three days and examine again in the 

 hanging drop for any forms of life present. 



13. Compare the flora of these two microscopical prep- 

 arations. Suggest why each type of organism is present. 



14. Compare all types of soil examined both quanti- 

 tatively and qualitatively as to their microflora. Which 

 soils are most alike in their flora? Suggest a reason why. 

 Why do various soils vary in the number of bacteria found? 



REFERENCES 



MARSHALL: Microbiology, pp. 226-245. 



CONN: Agricultural Bacteriology, pp. 34, 70, 120. 



EYRE: Bacteriological Technic. Second Ed., pp. 470-478. 



B. MICROSCOPICAL METHOD 



Apparatus. Soil or manure of same type as used for 

 plating; sterile water; sterile Chinese ink; platinum loop 

 of known capacity; sterile watch glass; cover-glasses, 

 absolutely clean] ocular micrometer; stage (object) microm- 

 eter. 



Method. 1. To 1 gm. of soil or excrement in a test 

 tube add 4 c.c. of sterile water and shake vigorously for 

 five minutes. 



2. Place 0.5 c.c. in a clean, sterile watch glass. Add 

 0.5 c.c. of Chinese ink. 



3. Mix with a platinum loop of known capacity. 



Note. To determine the capacity of the platinum loop, weigh 

 two watch glasses. Into one put exactly 1 gm. (1 c.c.) of water. 

 Transfer five loopfuls from the glass containing water to the empty 

 watch glass. 



Weigh each. Then determine the weight and also the volume 

 of one loopful. 



