Both the fowl and rabbit suffered from an experimental hakumai-byo show a decrease of their heart weights, their heart muscles being usually submited to the atrophy with a nuclear development. The microscopic appearance of the heart muscle fibre, however, is not quite similar in both the hakumai-byo animals. For the cardiac muscle fibrils of the fowl become thin paripassu the sarcoplasm decreases, while those of the rabbit become also attenuated but accompany no marked decrease of the sarcoplasm. On the other hand, both the hakumai-byo animals show a shrinkage of the nerve cell and a prolifiration of the connective tissue in the spinal ganglion. The development of the Golgi apparatus of such a shrinking cell is markedly inhibited and sometimes the apparatus disappears from the cell protoplasm. This change of the spinal ganglion cell as well as that of the heart muscle fibre is liable to become more remarkable with the process of beri-beri-like symptome, but it is not so manifest as to be decided the grade of the symptome by the microscopic specimen.