52                                Automatic Pipette.

(3) Once in six months the plunger of the record syringe may be faintly
smeared with vaseline.

(4) If at any time the head of liquid is lost, the system must be primed
by suction before it will pump.

(5) The valves may be tested occasionally by removing the beaker of
saline. When this is done, no drip should occur from the suction pipe in
valve cap A. If a drip occurs, it shows that the valves are either stuck or
perished. If the former, the flap must be freed, and if the latter new ones
can be made and fitted in a few minutes.