62 BACTERIOLOGICAL ANALYSIS. 



the upper end. Push over large end some rubber tub- 

 ing with a clip. To keep this pipette sterile during the 

 manipulations, place it in a flask of sterile water, kept 

 boiling. Before use, it is, of course, allowed to cool. 



1. (a) Add .1 cc. of the water to each of three lique- 

 fied gelatine and two agar tubes (kept at 42° 0). 



Pour into plates, and incubate the former at 20°C, 

 and the latter at 37°C. 



(b) Add .1 cc. of the water to each of three liquefied 

 gelatine tubes and two agar tubes. 



Pour into plates, place these in Novy's or Buchner's 

 jars for incubation, anaerobically. 



As soon as colonies appear on the agar and gelatine 

 plates, remove and examine. 



Note the number of colonies, counting the colonies 

 by dividing the plate surface into 16 equal segments, 

 and counting one or more segments. 



Contrast the growths aerobically and anaerobically, 

 both as to the number and character of the colonies. 

 Nearly all sewage and pathogenic bacteria are faculta- 

 tive anaerobes, while the ordinary water bacteria (saph- 

 rophytes) are aerobic. Hence a large growth on the 

 anaerobic plate is always suspicious. Good potable 

 water, as a rule, does not contain over 100 bacteria per 

 1 cc, but this may run up to 1,000 and yet water be 

 fairly good. Large numbers are always suspicious of 

 some form of organic pollution. 



Note the character of the colonies. Look for colon- 

 ies suspicious of Bacillus coli communis, and also for 

 liquefying forms. 



