^8 SOIL BACTERIOLOGY 



2. From the first 99-c.c. water blank make i-c.c. transfer 

 to a second and a third. 



3. Pour cellulose agar plates from the second and third 

 dilution. 



4. Incubate all of the plates under a bell jar at 28° C. 

 Very often the cellulose organisms do not appear for several 

 weeks. 



5. Look for the colonies with clear zones. 



Exercise 6 



Formation of Carbon Dioxid from Organic Substances 



1. For this exercise use a field soil and adjust the moisture 

 content to about half-saturation. 



2. Mix thoroughly so as to have the entire sample 

 uniform. 



3. Weigh into suction flasks (2-liter capacity) four equal 

 quantities of the soil, i kilo each, and treat as follows: 



(a) Untieated, 



(b) Add 2 per cent, of finely ground vegetable matter, clover, com, 



beet leaves, or something similar. 



(c) Add 2 per cent of air-dried and finely ground barnyard manure, 



(d) Add I per cent, of cane-sugar. 



4. Connect to a glass cylinder so arranged with glass 

 beads and alkali that the carbon dioxid (CO2) will be 

 caught as it is drawn through the solution. 



5. Every forty-eight hours determine the amount of 

 carbon dioxid by drawing a current of air through the 

 apparatus for twenty minutes with a water-pump (see page 

 150). Free the current of air from carbon dioxid by pass- 

 ing through strong N/i potassium hydroxid. In order to 

 regulate the air, count the number of air bubbles. 



