Fig. 5. Dialysis. The presence of protein molecules (large circles) induces a net movement of water (small dots) across the semipermeable membrane to the protein side. There is also a net movement of salt molecules (broken circles) away from the protein side. With the exception of protein, movement of all molecules occurs in both directions, but net movement is in the direction as indicated by the solid arrows. (Courtesy of RL Stamper, MD.)