244 GENERAL MICROBIOLOGY 



4. Transfer one loopful of the " ink manure " solution 

 to a clean, sterile cover-glass and spread in an even film 

 over the entire surface. 



5. Let this dry in air and fix by passing three times 

 through the flame. Mount at once in balsam. 



6. Measure the surface area of the cover-glass. Also 

 the diameter of one field of the oil immersion lens (using 

 the stage micrometer) and from that the area of the field. 



7. Count fifty fields and determine the average. 



8. From the data which you now have, determine the 

 number of organisms on the cover-glass, which is the number 

 in one loopful. 



9. Then from this calculate the number in 1 gm. of soil 

 or excrement. 



10. Also calculate the weight of bacteria in 1 gm. (See 

 p. 88, Marshall's Microbiology.) 



11. Compare the count thus obtained with the count 

 obtained by the plate method. What is shown? How 

 do you explain this result? 



12. Compare the manure and soil counts. Draw con- 

 clusions and explain. 



13. What other methods are used for obtaining numbers, 

 etc., of organisms in soil and like materials? 



14. State your data and observations in full. Draw 

 any conclusions warranted and point out any practical 

 applications. 



REFERENCES 



LOHNIS: Laboratory Methods in Agricultural Bacteriology, pp. 



89-91. 



LIPMAN and BROWN: Laboratory Guide in Soil Bacteriology, pp. 7-9. 

 MARSHALL: Microbiology, pp. 238-244. 



