APPENDIX. 333 



twelve test-tubes with blocks of potato. Sterilize all by 

 steam for one hour at 100 C. 



(b) Preparation of Sterile Beef-tea : Prepare 1000 c.c. of 

 beef-tea culture-fluid. Fill one dozen sterile test-tubes, with 

 one inch of the beef-tea in each, and sterilize them in the 

 steam sterilizer for one hour. 



Formula for nutrient beef-tea : 



Beef-extract, 2 grams ; 



Peptone, 10 " 



Salt, 5 " 



Water, 1000 c.c. 



(c) Preparation of Nutrient Gelatin: Prepare 1000 c.c. of 

 nutrient gelatin. Fill into sterile tubes as in the case of the 

 beef-tea and sterilize by the fractional method. Solidify with 

 tube in upright position. 



Formula for nutrient gelatin : 



Beef-extract, 2 grams ; 



Peptone, 10 " 



Salt, 5 



Gelatin, 100 " 



Water, 1000 c.c. 



(d) Preparation of Nutrient Agar : Prepare 1000 c.c. of 

 nutrient agar. Fill into test-tubes as in the case of gelatin 

 and sterilize. Solidify with tube in the inclined position. 

 The formula for agar is like that of gelatin, excepting that 10 

 grams of agar are substituted for the gelatin. 



EXPERIMENT 3 : Demonstration of Sterility, Infection, and 

 Contamination : Select three of the Petri saucers containing 

 sterile potato. Expose one of them to the air for five min- 

 utes, causing it to be contaminated. Another, infect by rub- 

 bing the finger over the laboratory desk and then across the 

 potato. The third allow to remain closed, so that it will 

 remain sterile. Label each dish properly. Notice the result 

 in the next few days. 



EXPERIMENT 4 : Study of a Mould : Select a well-developed 



