BACTERIOLOGICAL ANALYSIS OF SEWAGE 229 



6. Make an agar shake as in Exercise 1 and inoculate 

 lactose bile fermentation tubes with 0.1 c.c. direct and 1 

 c.c. of the 1 : 100 dilution of the sample respectively (or 



greater quantities if only 

 a small amount of pollu- 

 tion is suspected). 



7. Incubate the agar 

 shake, fermentation 

 tubes and agar plates at 

 37 C. Place gelatin 

 plates at 15 to 20 C. 



8. Make note of the 

 hour at which the cul- 

 tures are placed at 37 C. 

 Examine these within 

 twenty-four hours for in- 

 dications of the presence 

 of the colon-type of 

 organisms. 



9. Examine and count 



FIG. 50. General Ground Plan of Individual House Sewer System 

 Showing Exit from House, Anaerobic Tank, (A) Switch, and 

 (B) Subsurface Irrigation Tile. 



the agar plates after eighteen to twenty-four hours incuba- 

 tion at 37 C. (Keep at room temperature after forty- 

 eight hours.) 



