WATER 423 



water sample direct from the bottle; to the second, 

 0.3 c.c. ; and to the third, 0.2 c.c. ; and pour a plate 

 of each tube. To the fourth tube add 0.5 c.c. of the 

 diluted water sample from the capsule; to the fifth, 

 0.3 c.c. ; and to the sixth, 0.2 c.c. ; and pour a plate from 

 each. 



18. Label each plate with the quantity of the water 

 sample it contains that is, 0.5 c.c., 0.3 c.c., 0.2 c.c., 

 0.005 c - c -> 0.003 c.c., and 0.002 c.c. 



19. Pour a control (uninoculated) gelatine plate. 



20. Allow the plates to set, and incubate at 20 C. 



21. To the first tube of liquefied wort gelatine add 

 0.5 c.c. water sample; to the second, 0.3 c.c. ; and to the 

 third, 0.2 c.c. 



22. Label the plates, allow them to set, and incubate 

 at 20 C. 



23. Count and record the number of colonies that 

 have developed upon the agar at 37 C. after forty- 

 eight hours* incubation. 



24. Note the number of colonies present on each of 

 the gelatine and wort gelatine plates after forty-eight 

 hours' incubation. 



25. Replace the gelatine and wort plates in the 

 incubator; observe again at three days, four days, and 

 five days. 



26. Calculate and record the number of organisms 

 present per cubic centimetre of the original water from 

 the average of the six gelatine plates at the latest date 

 possible up to seven days the presence of liquefying 

 bacteria may render the calculation necessary at an 

 earlier date, hence the importance of daily observations. 



Method of Counting. The most accurate method 

 of counting the colonies on each of the plates is by 

 means of either Jeffer's or Fakes' counting disc. Each 

 of these discs consists of a piece of paper, upon which is 

 printed a dead black disc, subdivided by concentric 

 circles and radii, printed in white. In Jeffer's counter 



