The air-dried human blood smears are immersed in distilled water from 3 minutes to 40 days, and the water-solubility of the hematological granules, glycogen granules and of the peroxidase reaction substance in leucocytes are tested. The results of the experiments indicate the following two points.
1) The eosinotthil granules always resist dissolution in water for a longer period of time than do the neutrophil granules.
2) The peroxidase reaction is definitely preferable to other blood stainings not only for differential staining between myelogenous and lymphatic leucocytes, but also for demonstration of the leucocytes in the degenerating stages due to the hypotonic medium.