Figure 4 shows the basic set-up and procedure using a Buchner funnel with a 150-mm diameter perforated base plate (Scien- tific Equipment of Houston). To prepare the funnel as shown in Figure 4A, the membrane filter must be sealed to the bottom plate of the funnel. This is most easily accomplished by first run- ning a narrow bead of biologically safe silicone sealant (such as Factor II A-4100 or aquarium-safe silicone) around the bottom of the funnel just inside the 142-mm circumference of a mem- brane filter. Next, place the mesh screen loosely inside the bead. I recommend using a 120-mm diameter screen cut from a Buchner polyethylene disc (Avogadro’s Lab Supply, Inc.). Lastly, place the membrane filter on top of the bead and press down on the edge. I have used the top portion of 130-mm two-piece polypropylene Buchner funnel for this purpose (Avogadro’s Lab Supply, Inc.), but any ring of that approximate diameter should work well. After curing, this procedure yields a perfect seal, produces a sur- face of about 120 mm in diameter for attachment of the cells, and enables culture medium to flow uniformly across the membrane after inversion of the apparatus. The seal is easily removed with a razor blade for the next experiment.