Factors Affecting the Conversion of Yellow to Red Marrow

The tail vertebrae of the rat contain fatty marrow. The unamputated distal tail was implanted into the peritoneal cavity and disarticulated tail vertebrae were transplanted into the subcutaneous tissue of the abdomen in an effort to study the effect of environmental factors such as temperature and blood flow on the cellularity of the marrow. Transplantation alone increased only slightly the cellularity while the addition of phenylhydrazine treatment increased it greatly. These observations indicate that there is an inherent determinant of the cellularity of marrow in different sites, although this can be modified to a certain extent by environment and by physiologic stimulation.