Laboratory Outline for General Bacteriology 



EFFECT OF TEMPERATURE ON KEEPING QUALITY OF MILK 



Absolutely fresh milk of good quality is taken at 5 P. M. and 

 after mixing well is divided into three parts. These are kept at 

 5 C., 20 C., and 37 C. respectively for twenty hours. 



Make four litmus lactose gelatin and four agar plates from 

 each sample using the following dilutions for each medium : 



5 C 



200 200 100 100 



20 C. 

 100,000 100,000 50,000 50,000 



37 C 



1,000,000 1,000,000 500,000 500,000 



Incubate agar plates at 37 C. for two days. Count and find 

 the average number of bacteria per cubic centimeter for the three 

 samples. 



Incubate the litmus lactose gelatin plates at 20 C. for seven 

 days unless liquefiers threaten to destroy the plates when they 

 should be counted sooner. Count total number of bacteria, acid 

 bacteria (those that turn litmus around them pink) and liquefying 

 bacteria. Calculate the average number per cubic centimeter for 

 total bacteria, acid bacteria, and liquefying bacteria. 



How do the total numbers on agar and gelatin compare? 



BACTERIA FROM VARIOUS SOURCES 



The purpose of these experiments is to show the abundance 

 of bacteria in their relation to our everyday life. 



1. Wash hands in pan containing 1000 cc. of sterile water. 

 Plate using 



1 cc. .5 cc. .2 cc. .1 cc. 



2. Wash hands carefully with soap under tap then without 

 drying them or touching anything wash again in a second pan con- 

 taining 1000 cc. of sterile water. Plate using 



1 cc. .5 cc .2 cc. .1 cc. 



3. An apparently clean wash bowl is washed with a sterile 

 brush and 1000 cc. of sterile water. Plate using 



1 cc. .5 cc. .2 cc. .1 cc. 



4. Place a pencil in test tube with 10 cc. of sterile water. 

 Wash pencil well and plate using 



1 cc. .5 cc. .2 cc. .1 cc. 



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