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Objectives-To determine optimal site for collection of bane marrow from desert tortoises, and to characterize cytologic staining and morphologic features of bone marraw hematopoietic cells.

Animals-16 desert tortoises.

Procedure-Bone marrow was obtained at necropsy from the pelvis, proximal portion of the humerus, femur, and thickened portions of the cranial to craniolateral and caudal to caudolateral margins of the carapace and plastron for histologic and cytologic examinations. Cytocentrifuged preparations of marrow cells were evaluated for reactivity to cytochemical stains.

Results-Histologic sections were adequate for evaluating acidophils, acidophil precursors, and erythrocyte precursors, it was difficult to differentiate among monocytes, lymphocytes, thrombocytes, and blast cells, and eosinophils could not be differentiated from heterophils, Basophils were in rare, smart clusters of 3 to 12 cells. A few lymphoid follicles were found in the pelvis and long bones.

Use of cytochemical staining accomplished differentiation between agranular heterophil precursors and granulated heterophils, and between granulated eosinophils and basophils. Monocytes, azurophils, and monoblasts had similar staining features. Staining of erythrocyte precursors with Sudan black B differentiated them from lymphocytes. Only a few small cells with periodic acid-Schiff-positive cytoplasm were identified as thrombocytes. Lymphocytes did not stain with any of the cytochemical stains.

Conclusions-For histologic and cytologic evaluation of bone marrow hematopoietic cells, pelvis, proximal portion of the humerus, femur, and thickened portions of the peripheral cranial and caudal regions of the carapace and plastron are suitable sites to collect specimens. There are distinct cytochemical markers for heterophil, monocyte, and erythrocyte precursors, as well as later stage heterophils, eosinophils, basophils, monocytes, and azurophils.