Laboratory Outline for General Bacteriology 



are made on the chart in the blank space with heading "Medium 

 solid." 



NUTRIENT BROTH 



Nutrient broth is made from beef extract, peptone, and distilled 

 water. After inoculation the nutrient broth cultures must be 

 handled carefully to avoid shaking down any pellicle or surface 

 growth that may be present. After recording surface growth and 

 clouding, which may be distinguished better by comparison with 

 an uninoculated tube, the character of the sediment may be deter- 

 mined by giving the tube a whirling motion and observing. 



AGAR PLATES FOR COLONY DESCRIPTIONS 

 AND SUNLIGHT TEST 



Inoculate a water blank with a small amount of culture taken 

 from the original agar slants. Shake, and with a sterile loop trans- 

 fer once from water blank to a tube of melted agar. Shake agar 

 without having medium touch the cotton plug. Sterilize loop and 

 make two transfers from first agar tube to a second. Pour both 

 agar tubes into plates marking them "a" and "b" in addition to 

 the culture number. When cool paste a thick opaque paper over 

 one-half the bottom of each plate. This is to shut off the light. 

 Expose plates to the sunlight for fifteen minutes, watching to see 

 no shadows creep over them. Place in locker to incubate. After 

 seven days make descriptions of both surface and deep colonies 

 from the plate that shows the most favorable number of bacteria. 



To determine the percentage of bacteria killed by sunlight 

 count an equal area on both the shaded and sun exposed portion 

 of the Petri dish. Subtract the number of bacteria in sun exposed 

 area from the number in the shaded area and divide by the number 

 of bacteria in the shaded area. 



Example. Number of bacteria in shaded area 28, number in 

 sun exposed are 12. 2812=16 16-28=57.1 The result is 

 approximately 57 per cent. 



GELATIN PLATES 



These are made in the same manner as the agar plates but 

 are not exposed to sunlight. Incubate in the locker right side up. 

 Liquefying bacteria must be watched carefully to get descriptions 

 before the gelatin is entirely liquefied. 



NITRATE BROTH 



Nitrate broth is a medium made by using small amounts of 

 peptone and potassium nitrate in tap water. After cultures have 



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