Abstract
The significance of tracer-experiments as the basis of the theory of vesicular transport or cytopempsis in the capillary endothelium was re-examined. Labeling by ferritin was studied under the electron microscope in the muscle capillaries of the rat and the mouse which were fixed beforehand by perfusion with glutaraldehyde or with OsO4. Virtually all caveolae and vesicles of the endothelium were labeled by ferritin-particles. Ferritin was also found in the pericapillary space and basement membrane.
The previous tracer-experiments are believed to indicate not an active membrane flow of cells but only a dispersion of particulate substances through the extracellular spaces and into the vesicular structures of cells opening to them.
