The brains and spinal cords from thirty-six pigs infected with the bog cholera virus of ALD strain were crossly sectioned into ten thin slices of frontal Jobe, optic chiasmus, corpus mammilare, cerebral peduncle, pons, cerebellum, medulla oblongata, thalamus, hypophysis, and spinal cord. The former eight slices were also sectioned into two slices of right and left side. So each case was sectioned into eighteen pathological slides. The microscopic findings from these pathological slides were as follows :
1. The microscopic changes mainly appeared with perivascu!ar infiltration (perivascular cuffing or non··suppurative encephalitis), microgliosis, perivascular hemorrhage, degeneration of the endothelial cells, increasing and margination of intravascular white blood cells, leptomeninge infiltration, and vascular congestion. Although the frequency of non-·snppurative encephalitis lesion was 90%but not reacheed to 100%，yet degeneration of the endothelial cells and perivascular hemorrhage were all 100%. So hog cholera can be accurately diagnosed by histopathologiclal examination.
2. In these microscopic examination, the main characteristics were the nonsuppurative encephalitis, degeneration of the endothelial cell, perivascular hemorrhage and microgliosis. The non··suppurative encephalitis mainly appeared on thalamus, medulla oblongata and cerebral peduncle area; the degeneration of the endothelial cells on thalamus, cerebral peduncle area, medulla oblongata and corpus mammilare area; the perivascular hemorrhage on corpus mammilare and optic chiasmus area ; the microgliosis on corpus mammilare and cerebral peduncle area.
3. The microscopic lesions between right and left side of brain showed no remarkalbe difference. Only swelling of the endothelial cell and perivascular hemorrhage were slightly high frequency on the right side.
4. Among the ten different sections of each; case mentioned above, the non suppurative encephalitis lesion was seen only in one section, i.e. 2.8% of all cases.
5. In order to understand the onset of the non--suppurative encephalitis, four pigs were employed in this experiment. The results showed that the nonsuppurative encephalitis presented when moderate clinical signs appeared and neutrophi!es shifted to left.