PASTEURIZATION 203 



9. Give all data and results in full. Draw any conclu- 

 sions possible and point out any practical applications. 



REFERENCES 



HITE, B. H., GIDDINGS, N. J., and WEAKLEY, CHAS. E.: The effect of 

 pressure on certain microorganisms encountered in the preservation 

 of fruits and vegetables. Bui. 146, W. Va. Univ. Agr'l Expt. Sta., 

 1914. 



MARSHALL: Microbiology, pp. 159-161. 



LAFAR: Technical Mycology, Vol. I, pp. 79-84. 



FISCHER: Structure and Functions of Bacteria, pp. 75-77. 



EXERCISE 25. TO DETERMINE THE EFFECT OF PAS- 

 TEURIZATION UPON THE GROWTH OF MICRO- 

 ORGANISMS 



Apparatus. 300 c.c. each of milk (not sterile) and of 

 some fermenting fruit juice; water bath; two thermometers; 

 four sterile 200 c.c. Erlenmeyer flasks; twenty-four tubes 

 of dextrose agar; dilution flasks; twenty-four sterile Petri 

 dishes; sterile 1 c.c. and 10 c.c. pipettes. 



Method. 1. Place 150 c.c. of milk in each of two 200 c.c. 

 sterile Erlenmeyer flasks; do the same with the fruit juice. 



2. Make three dilution plates each (1-100, 1-10,000, 

 1-1,000,000) from the milk and from the fruit juice in agar 

 and incubate (inverted) at room temperature. 



3. Place a flask of each nutrient liquid in the water bath 

 (cold water) and heat rapidly to 75-80 (thermometer in 

 each flask), shaking the flasks frequently to obtain an even 

 temperature throughout their contents. 



4. Remove the flasks when the temperature reaches 80 

 C. and cool* them quickly. 



5. Make dilution plates (1-10, 1-1,000, 1-10,000) in 

 agar; mark each carefully. Place the flasks and plates at 

 room temperature. 



6. Place the other two flasks in the water bath (in cold 

 * It has been found by experiment that the quick cooling must take 



place through the temperatures 40-36 C. in order to be most efficient 

 in preventing further bacterial growth. 



