168 LABORATORY GUIDE IN BACTERIOLOGY 



EXERCISE 4. DETERMINATION OF THE* NUMBER OF 

 SPORES IN SOIL 



1. Add i c.c. of the soil suspension 1:1,000 to a 

 tube of melted gelatin. 



2. Heat the tube in a water bath to 80 C. for 10 

 minutes. 



3. Pour the gelatin on a petri dish and incubate 

 at room temperature for three or four days. 



4. Count the colonies and calculate the number 

 for one gram dry soil. 



Each colony represents one spore originally present 

 in the soil. 



SECTION 2 



A STUDY OF THE PEPTONIZATION OF PROTEINS BY 

 SOIL BACTERIA 



EXERCISE I. DIGESTION OF BLOOD SERUM 



1. Place 200 c.c. blood serum in a 500 c.c. flask 

 and sterilize in the autoclave. 



2. After cooling, add 5 c.c. of a suspension of garden 

 soil in water. 



3. Incubate at 37 C. until all of the serum has been 

 liquefied. 



EXERCISE 2. DETERMINATION OF THE CHANGES PRO- 

 DUCED IN BLOOD SERUM 



1. Add a suitable quantity of distilled water to the 

 liquefied blood serum. 



2. Filter to remove bacterial masses and impurities. 



3. Neutralize with NaOH, using litmus as indi- 

 cator. 



