The author has carried out some observations about rabbits at 450mmHg pressure in low pressure chamber and has obtained the following results. 1) The number of red corpuscles in the peripheral blood vessel increases 7-20% per cubic millimeter. 2) The haemoglobinvalue also increases with the red corpuscle but the former is a little fewer than the latter. 3) The body temperature expresses no remarkable change. 4) The capillary blood vessel of ear increases the width of, it. 5) The following fact is experimentaly proved at normal pressure that the number of red corpuscles in thicker blood vessel is greater than that in smaller blood vessel. 6) The spleen which is fined outside the abdomen contract at low barometric and oxygen pressure. For some days after spleen extirpation, the increase of red corpuscles at low pressure is not to be seen or very slight but on 49th day red corpuscles increase under low pressure as much as normal rabbit. 7) Injektion of pilocarpin. into vein increases the number of red corpuscles, and injektion of adrenalin and atropin decreases of it. From the above mentioned facts the auther recognized as principal cause the change of distribution of red corpuscles following the dilatation of peripheral blood vessels under low pressure.