Models for drug delivery are based on the use of stirred tanks to represent organs that contain no mass transfer resistances. In the original Krogh cylinder model, a mass transfer resistance shows up but there is no convection in the tissue where convection should matter. In the present study, a two-dimensional flow field is used to show that when a liquid enters the capillary, some leave through the walls into the tissue at the arterial end and then doubles back into the capillary at the venous end. Some flow does not return which is taken to be the flow to the lymphatic system. We can get the measured transcapillary pressure drop of about 2,666 Pa if in addition the compliance of the tube wall is taken into account. Very realistic flow fields have been shown for a model liver and a tumor.