. A laboratory guide in elementary bacteriology. Bacteriology. CHAPTER V. BACTERIOLOGICAL ANALYSIS. EXERCISE LXV. COMPARATIVE ANALYSIS OF AIR (Koch's flethod). a. Plate three tubes of gelatin and expose by removing lid for 20 minutes in the following places: 1. Laboratory, 2. Cellar, 3. Out of doors. 6. Replace the lids and keep plates at 22° C. for several days. c. Count the colonies; if the number of colonies is greater than 100, use the counting plate figured in Plate I. A. and count a portion and estimate the whole number. d. Calculate the area of the Petri dish by multiplying the square o
. A laboratory guide in elementary bacteriology. Bacteriology. CHAPTER V. BACTERIOLOGICAL ANALYSIS. EXERCISE LXV. COMPARATIVE ANALYSIS OF AIR (Koch's flethod). a. Plate three tubes of gelatin and expose by removing lid for 20 minutes in the following places: 1. Laboratory, 2. Cellar, 3. Out of doors. 6. Replace the lids and keep plates at 22° C. for several days. c. Count the colonies; if the number of colonies is greater than 100, use the counting plate figured in Plate I. A. and count a portion and estimate the whole number. d. Calculate the area of the Petri dish by multiplying the square of the diameter by e. Express the results in terms of the number of organisms which fall per square foot per minute. This method enables one to make a rough comparison of the number of organisms occurring in the localities examined, but to determine the number per volume the fol- lowing method must be employed. References. H. 390. QUANTITATIVE DETERMINATION OF NUHBER OF BACTERIA IN AIR (PetrNSedgwick Method).. EXERCISE LXVI. General Directions. a. A piece of glass tubing 6 mm. (fin.) in diameter by 15 cm. (6 in.) long is drawn out at one end in a gas flame and sealed. h. Fill this tube about one-third full with granulated sugar, insert a cotton plug next o.: to the sugar and one at the end of the tube (). c. Sterilize in the hot air sterilizer for A- 1 and Yz hours at 130° C. (sugar melts at a higher temperature). V>. d. Fasten the tube, pointed end up, in a clamp, remove the first cotton plug and con- nect with an aspirator. (Fig. 14). e. Break off the pointed end of the tube _ and draw a measured quantity of air through fig. is. Apparatus for fii the sugar. tering air through sugar. Special Directions. a. Filter 50 liters of air. 6. Dissolve sugar in 10 cc. of sterile water and make plates, using 1 cc. of the Fig. 14. Aspirator for filtering air. A, ready for sterilization. B, point broken off and at- tached to aspirator. mixture. c. Incubate, count colonies
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