In current theories of immunity it is implied that all organs, tissues and cells of the animal body are equally permeable to any given antigen, topographic distribution being determined solely by hypothetic hereditary specific intracellular avidities. For three decades, therefore, immunology has ignored the possibility that relative permeability may play a part in immunologic adaptation. With the newer immunology,5 however, in which specific antibodies are not pictured as desquamated preformed "receptors" but as entirely new biochemical complexes presumably synthesized as a result of interactions between injected antigens and normal tissue components, relative permeability becomes a primary factor in topographic distribution and subsequent antibody synthesis. Immunologists, therefore, welcome the current researches of Drs. Rous, Gilding and Smith6 of the Rockefeller Institute, the most important feature of which is their ingenious technic, adaptable to so many basic investigations.
In their study of vascular permeability, the Rockefeller Institute physiologists used selected