Quantitative investigation of stem cell candidates in the bone marrow of growing guinea pigs.

Possible candidates for hemic stem cells were studied in a quantitative investigation of the bone marrow of growing guinea pigs. The stem cell candidates were classified as lymphoid cells of types I-IV, roughly corresponding to small lymphocytes, large lymphocytes, micromyeloblasts and myeloblasts of other authors. The cellular content of the bone marrow of guinea pigs of three different ages was determined. All types of nucleated cells per femur were found to increase with age. When the cellular content was related to the body weight, a peak number of lymphoid cells was found in the intermediate age group with the exception of the lymphoid cells of type III, which reached its peak in the oldest animals. This cell type has been suggested by Dicke et al. as the probable stem cell responsible for colony formation.