Abstract
The uptake of horseradish peroxidase was studied in the duodenum of fasting mice. Five, 7 or 3 x 5 mg were injected in the tail vein. The protein rapidly diffused into the intercellular spaces of the villus and crypt epithelium. Subsequently, the marker was segregated in the dense bodies of the absorbing cells, particularly in the apical part of the cells. The tracer was never observed in the lumen of the gut but was blocked at the zonula occludens or degraded in the dense bodies. A diffuse staining of some cells was observed, and control experiments were made to test the possibility of artifacts.