7. Drain off the water and immerse tubes in a large jar containing water acidulated with 2 to 5 per cent. hydrochloric acid. Allow them to remain there for about fifteen minutes. 8. Remove from the acid jar, drain, rinse thoroughly in running water, then with distilled water. 9. Invert the tubes and allow them to drain completely. Dry the tubes and polish the glass inside and out with a soft cloth, such as selvyt. ~Infected flasks, plates, and capsules~ must be treated in a similar manner. ~Flasks~ which have been used only in the preparation of media must be cleaned immediately they are finished with. Fill each flask with water to which some soap powder and a few crystals of potassium permanganate have been added, and let boil over the naked flame. The interior of the flask can then usually be perfectly cleaned with the aid of a flask brush, but in some cases water acidulated with 5 per cent. nitric acid, or a large wad of wet cotton-wool previously rolled in silver sand, must be shaken around the interior of the flask, after which rinse thoroughly with clean water, dry, and polish. ~Infected Pipettes.~-- 1. Plunge infected pipettes immediately after use into tall glass cylinders containing a 2 per cent. solution of lysol, and allow them to remain therein for some days. 2. Remove from the jar and drain. Boil in water to which a little soap has been added, for thirty minutes. 3. Rinse thoroughly in cold water. 4. Immerse in 5 per cent. nitric acid for an hour or two. 5. Rinse again in running water to remove all traces of acid. 6. Complete the cleaning as described under "new pipettes." When dealing with graduated capillary pipettes employed for blood or serum work (whether new or infected), much time is consumed in the various steps from 5 onward, and the cleansing process can be materially hastened if the following device is adopted. Fit up a large-sized Kitasato's filter flask to a Sprengel's suction pump or a Geryk air pump (see page 43). To the side tubulure of the filter flask attach a 20 cm. length of rubber pressure tubing having a calibre sufficiently large to admit the ends of the pipettes. Next fill a small beaker with distilled water. Attach the first pipette to the free end of the rubber tubing, place the pipette point downward in the beaker of water and start the pump (Fig. 22). [Illustration: FIG. 22.--Cleaning blood pipettes.] When all the water has been aspirated through the pipette into the filter flask, fill the beaker with rectified spirit and when this is exhausted refill with ether. Detach the pipette and dry in the hot-air oven. ~Slides and cover-slips~ (Fig. 23), when first purchased, have "greasy" surfaces, upon which water gathers in minute drops and effectually prevents the spreading of thin, even films.