422 BACTERIOLOGICAL ANALYSES 



Suck up rather more than i c.c. into the pipette and 

 allow the pipette to empty ; this moistens the interior of 

 the pipette and renders accurate measurement possible. 

 Now draw up exactly i c.c. into the pipette. Withdraw 

 the pipette from the bottle, replace the stopper, and 

 stand the bottle upright. 



7. Take the first melted agar tube in the left hand, 

 remove the cotton-wool plug, and add to its contents 

 0.5 c.c. of the water sample from the pipette; replug 

 the tube and replace it in the water-bath. In a similar 

 manner add 0.3 c.c. water to the contents of the second 

 tube, and 0.2 c.c. to the contents of the third. 



8. In a similar manner add i c.c. of the sample to the 

 contents of the fourth tube. 



9. Similarly, add 0.5 c.c. and o.i c.c. respectively to 

 the contents of the fifth and sixth tubes. 



10. Drop the pipette into the cylinder containing 

 lysol solution. 



11. Mix the water sample with the medium in each 

 tube in the manner described under plate cultivations ; 

 pour a plate from each tube. Label each plate with 

 (a) the distinctive number of the sample, (b) the quan- 

 tity of water sample it contains, and (c) the date. 



1 2 . Pour the contents of a tube of liquefied agar 

 not inoculated into a Petri dish to act as a control to 

 demonstrate the sterility of the batch of agar employed. 



13. Allow the plates to set, and incubate at 37 C. 



14. Empty the water chamber of the levelling appa- 

 ratus and refill it with ice-water. 



15. By means of the sterile 10 c.c. pipette deliver 

 9.9 c.c. sterile distilled water into a sterile glass 

 capsule. 



1 6. Add o.i c.c. of the water sample to the 9.9 c.c. 

 sterile water in the capsule. This will give a dilution 

 of i in 100. 



17. Plant the six tubes of nutrient gelatine in the 

 following manner: To the first tube add 0.5 c.c. of the 



