EXERCISES IN SOIL BACTERIOLOGY 



SECTION I 



NUMBER OF MICROORGANISMS IN SOIL 



Directions for Drawing Soil Samples 



When it is necessary to secure accurate samples, dig a 

 ditch to the desired depth. By means of a sterile trowel 

 representative samples may be drawn from the sides of the 

 ditch. In this way outside contamination is largely pre- 

 vented. 



Samples from the surface to i foot deep may be taken as 

 follows: Remove the coarse surface d6bris and sink a 

 large, sterile test-tube or metal cylinder to the desired 

 depth. Samples of surface soil may be taken with a sterile 

 spatula. Draw several samples and empty into^ sterilized 

 paper bags or other vessels. Mix and pulverize the sample. 

 This may be done with a sterile spatula upon a large piece 

 of sterile paper. From the well-mixed sample remove a 

 representative portion for dilution, and at the same time 

 make a moisture determination. As soon as possible 

 after samples are drawn arrange to count. 



Exercise i 



Number of Bacteria According to the Dilution Method 



I. Add <o grams of soil to <oo c.c. of sterile water or^ 

 500 C.C. of physiologic salt solution. 



x6 



