130 GENERAL BACTERIOLOGY 



Quantitative Analysis. 



a. After shaking the sample at least 25 times remove 1 ce. of 

 the water by means of a sterile pipette and place it in the bottom of a 

 sterile Petri dish. In the same way remove % cc. and y j- cc. Pipettes 

 graduated to ^Vths. may be used, or a 1 cc., or even a 5 cc. pipette 

 may be used by counting the whole number of drops delivered and 

 then taking the number of drops to make the required fraction. If 

 the sample be supposed to be highly infected it should be diluted 

 with sterile water before the cultures are made. Plates ought not 

 to contain over 200 colonies. 



. b. Pour into the dishes fluid gelatin (not warmer than 42° C.) 

 and tip them from side to side until the medium and water are 

 thoroughly mixed. Solidify and incubate at 22° C, or below. 



c. In the same way make agar plates using ordinary agar or, 

 better, 5% glycerine agar. Incubate at 22° C. 



d. Count the colonies at the end of 48 hours as directed above 

 (66 c.) and at intervals afterward until the maximum number of 

 colonies is obtained. Express the results in the number of bacteria 

 per cc. of water. 



Qualitative Analysis. 



a. Number of species. Examine carefully, under the low power 

 of the microscope, the plates made above to determine the number 

 of different species, describing each very briefly. Estimate also the 

 total number of liquefying organisms per ce. 



b. Tests for Fecal Bacteria (B. coli) as follows: 



1. Fermentation tube test. Inoculate three fermentation tubes, 

 containing 1% dextrose bouillon, with y^i 1> and 10 cc. of water 

 and incubate at 38° C. Tubes which develop from 30 to 70% of 

 gas should have lactose litmus agar plate cultures made from them 

 and then the gas formula may be determined. For B. coli it will 

 be about : CO^ : H : : 1 : 2 or CO, _ 1 



2. Iinlol test. Tubes of sugar-free bouillon or Dunham's solu- 

 tion inoculated and incubated at 38° C. for 4 to 5 day.s will show 

 the presence of indol if B. coli be present. 



3. Acid colonies. A lactose litmus agar plate should be made 



