3. Place the agar tubes in boiling water until the medium is melted, then transfer them to the water-bath regulated at 42° C. Liquefy the nutrient gelatine and wort gelatine tubes by immersing them in the same water-bath. 4. Remove the bottle containing the water sample from the ice-box, distribute the bacterial contents evenly throughout the water by shaking, cut the string securing the stopper, and loosen the stopper, but do not take it out. [Illustration: FIG. 206.--Withdrawing water from water sample bottle.] 5. Remove one of the 1 c.c. pipettes from the case, holding it by the plain portion of the tube. Pass the graduated portion twice through the Bunsen flame. Tilt the bottle containing the water sample on the bench holding the neck between the middle and ring fingers of the left hand; grasp the head of the stopper between the forefinger and thumb, and remove it from the bottle. 6. Pass the pipette into the mouth of the bottle, holding its point well below the surface of the water (Fig. 206). Suck up rather more than 1 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 1 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 1 c.c. of the sample to the contents of the fourth tube. 9. Similarly, add 0.5 c.c. and 0.1 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 quantity of water sample it contains, and (c) the date. 12. 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 apparatus 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. 16. Add 0.1 c.c. of the water sample to the 9.9 c.c. sterile water in the capsule. This will give a dilution of 1 in 100.