Scanning electron and light microscope correlation of individual human bone marrow cells before and after culture in nutrient agar.

This study was undertaken with the aim of identifying the different cell types found in human bone marrow by examining their surface morphology. In an attempt to obtain a homogeneous cell population, cells were both fractionated by discontinuous albumin density gradient centrifugation (DADGC) and selectively grown in nutrient agar. Both cell preparations underwent the critical point drying technique before examination under both the scanning electron microscope (SEM) and subsequently the light microscope (LM). When the SEM image of individual cells was compared with the corresponding LM image, it was not easy to identify the different cell types, because of the shrinkage and distortion that occurred during their preparation. The shrinkage observed under the SEM amounted to a 45% reduction in mean cell diameter. This shrinkage was confirmed by comparing the SEM and LM images of the same cell. Although shrinkage occurred throughout the dehydration sequence, critical point drying was responsible for a 25% reduction in mean cell diameter. Furthermore, direct observation under LM of fixed cells drying in air from ethanol, revealed visible contraction of the cell and distortion of the cell membrane. We assume that a similar morphological change occurred during critical point drying. We conclude that the shrinkage and distortion, caused by the dehydration process involved in SEM preparation, severely limit the value of a study of surface morphology by SEM in the identification of the different cell types found in human bone marrow.