Factors Affecting the Conversion of Yellow to Red Marrow

The tail vertebrae of the rat contain fatty alone increased only slightly the cellu-marrow. Tile unamputated distal tail was larity while the addition of phenylhydra-implanted into the peritoneal cavity and zine treatment increased it greatly. These disarticulated tail vertebrae were trans- observations indicate that there is an in-planted into the subcutaneous tissue of herent determinant of the cellularity of the abdomen in an effort to study the marrow in different sites, although this effect of environmental factors such as can be modified to a certain extent by temperature and blood flow on the cellu- environment and by physiologic stimula-laritv of the marrow. Transplantation tion. r[iTE CONVERSION OF RED TO YELLO\V MARROW in the extremities I diiriiig iclult life has been the subject of investigation and speculatioll for s-ears. Ternis such as “involution, ” “senescence,”1 and “atrophy’2 have been used to ellaracterize the 1)henonleflOll, but the cause and mechanism of the conversion still remain obscure. The reverse of this phenomenon, the con-version of normally yellow marrow back to red llas also been an interestin