1. Ectromelia virus, though it is panorganotropic, in cases of intraperitoneal and intracutaneous inoculations accompanies some pathological findings of r. e. s. (reticuloendothelial system). That reminds us the phagocytic activity of r. e. s. in case of the itnravenous injection of carbon particles. From this fact we can presume an occurance of viremia soon after the inoculation.2. The pathological findings in this infection, may be understood as a combination of the specific organotropy (including epithelial and mesenchymatous cells) and the inspecific attack to r. e. s.3. For this reason we are able to produce various forms of organ infection, according to the modus and dosis of the virus inoculation.4. For instance, through intraperitoneal inoculation, liver changes resembling the human hepatitis infectiosa can be elicited. We can observe analytically some processes of viral hepatitis with such an experiment.5. On the contrary, the change of the liver in the animals infected to their hind-foot, is more or less circumscribed and accompanies a rapid monocytic reaction around the foci. Such a focus contains scattered necrotic liver cells.6. In case of a slight infection of the hindfoot through a small virus dosis, by which we can expect the surviving of the animals through immunity, the viremic foci in liver, spleen and lymphncdes turn to healing after 6 days (lethal-infected animals surviue only 6 days), during which the cells with inclusion bodies fall into necrosis and disappear in a few days. The only exception in this case is the hind-foot, where the inclusion bodies remain till to the day (the 12th day) of the gangrenous separation of it, by which the infected epidermis accompanying some “healthy tissue-islet” of epidermis is lost together with it. This phenomenon may be well understood as an allergic reaction in form of the Arthus's phenomenon.7. The first stage of viral invasion proceeds as a degeneration of infected cells without cellular infiltration, thereafter appears a more or less monocytic reaction around it, The neutrophilic reaction appears with the accompanyment of vascular allergy. These processes are common as far as concerns to liver, spleen, lymph nodes, skin etc.8. A specific and characteristic finding in the case of the animals cured through immunity, is the fact of the prominent plasma cell reaction in spleen and lymph nodes.9. In the experiments with ectromelia virus, we recognised morphologically for the first time the fundamental procedure of immunopathology in viral disease.