Ultrastructure research in biology before the introduction of the electron microscope

Summary Before the introduction of the electron microscope for cytological research around 1940, indirect methods were used for disclosing sublight‐microscopic structures. The results obtained by macromolecular chemistry were combined with those from investigations made with polarized light and by X‐ray diffraction. The application of Wiener's theory of composite bodies proved the presence of rodlet and lamellar ultrastructures, and the X‐ray analysis gave information on the crystallinity and the size of the components of such structures. Both methods are based upon regular periodicities in the object investigated, so that their application is limited. Nevertheless, most of the conclusions concerning ultrastructural morphology gained with these techniques were corroborated when direct images of the relevant ultrastructures could be produced by electron microscopy.