SEWAGE 467 



quantitative examination and transmitted in the ice 

 apparatus used in packing those samples. 



Apparatus Required. As for water (vide page 420) . 



METHOD. 



1 . Arrange four sterile capsules in a row and number 

 them I, II, III, IV. 



2. Pipette 9 c.c. sterile bouillon into capsule No. I. 



3. Pipette 9.9 c.c. sterile bouillon into capsules II, 

 III, and IV. 



4. Add i c.c. of the sewage to capsule No. I by means 

 of a sterile pipette, and mix thoroughly. 



5. Take a fresh sterile pipette and transfer o.i 

 c.c. of the mixture from No. I to No. II and mix 

 thoroughly. 



6. In like manner transfer o.i c.c. from No. II to 

 No. Ill, and then o.i c.c. from No. Ill to No. IV. 



Now i c.c. of dilution No. I contains o.i c.c. of the original sewage, 



i c.c. of dilution No. II contains o.ooi c.c. of the original sewage, 



i c.c. of dilution No. Ill contains o.ooooi c.c. of the original sewage, 

 i c.c. of dilution No. IV contains o.ooooooi c.c. of the original sewage. 



7. Pour a set of gelatine plates from the contents 

 of each capsule, three plates in a set, and containing 

 respectively 0.2, 0.3, and 0.5 c.c. of the dilution. 

 Label carefully; incubate at 20 C. for three, four, or 

 five days. 



8. Enumerate the organisms present in those sets 

 of plates which have not liquefied, probably those 

 from dilution III or IV, and calculate therefrom the 

 number present per cubic centimetre of the original 

 sample of sewage. 



Qualitative. The qualitative examination of sewage 

 is concerned with the identification and enumeration 

 of the same bacteria dealt with under the corresponding 

 section of water examination ; it is consequently con- 

 ducted on precisely similar lines to those already in- 

 dicated (vide pages 426 to 441). 



