A new method for the simultaneous presentation of low and high magnifications of microscopic specimens: application to in vivo studies of mesenterial capillaries.

By combining an incident light microscope (C. Zeiss) with an inverted camera microscope (ICM 405, C. Zeiss) having a common optic axis, it was possible to present simultaneously two microscope images of one object. These images were recorded by two television cameras and displayed on a single monitor with the aid of a video mixer (Pieper, Schwerte). This method was applied to intravital microscopy of mesenterial capillaries (rabbit and frog). It allowed the choice of a vascular network as an overview with the incident light microscope from which a suitable capillary segment for an electrical stimulation experiment could be selected and magnified with the transmitted light microscope. The results of its application provided proof that electrically induced constrictions in capillaries are independent of proximally or distally occurring vascular reactions. Capillaries of mesenteries in rabbits and frogs were stimulated with direct currents ranging from +0.015 micro A to +20 micro A. The constrictions were found to be reversible and reproducible. In addition capillary constrictions could also be produced by topical application of histamine and serotonin droplets applied to the surface of the mesentery. These observations may help to resolve the question of whether capillary contractility in the sense of Stricker (1865, 1876) is a biological mechanism.