The normal human bone marrow was cultured in vitro by the clinical tissue culture method devised in our Department in order to see the influences of such factors as the medium temperature, the hydrogen ion concentration, the osmotic pressure in the media, and some single media, on the degenerative changes of neutrophils appearing in the growth area. These results were compared with those in the case of neutrophils cultured in the normal medium. The following are the conclusions. 1. In general the degenerative changes of neutrophils proceed slowly under low temperature but more rapidly at higher temperature. At 15℃ the progress is most slow while on the contrary, at the temperature below 10℃ it is rapid, The number of degeneration granules, vacuoles, and abnormal processes decreases as the bone marrow is cultured at a lower or at a higher temperature centering around 37℃-39℃. More condensed nuclei can be observed at a high temperature, and also at a low temperature. The eruption of the nucleus appears more frequently at low temperature, however, there is almost no nuclear eruption at high temperature. 2. As for the influence of the hydrogen ion concentration, the further away is the pH from that of the normal medium the more rapid is the degenerative changes. In the acid medium the appearance of small degeneration granules is more rapid but the number of vacuoles and sbnormal processes is less, showing no tendency of fusion of nuclear lobes but a strong tendency of non-homogeneous pyknosis. In alkaline medium degeneration granules are less but vacuoles and blisters are numerous, and cytoplasm is swollen, and nucleus tends to swell up or to erupt. 3. As for the influence of the osmotic pressure, in the isotonic solution the degenerative changes appear most slowly, and in the hypotonic solution the swelling of specific granules is marked and degeneration granules are numerous and large with many vacuoles. Cytoplasm and nulcleus are swollen, especially the eruption of the nucleus is striking. In the hypertonic solution the swelling of specific granules is observed, but the number and the size of degeneration granules are small. Vacuoles and abnormal processes are less, while myelin forms can be recognized relatively many. The nucleus and cytoplasm are condensed at the initial stage of the culture but later both of them are swollen. 4. In the single medium such as physiological saline solution, Ringer's solution, serum, or in the isotonic glucose solution, the degenerative changes proceed radidly at an early stage in any of these media, and the changes progress most rapidly in the glucose solution followed by physiological saline solution and Ringer's solution. The progress is slowest in the serum medium but it is more rapid than in the normal medium.