MATERIALS AND METHODS

Female mice (C57Bl 9 X DBA 8’) F1, bred in our laboratory from parent strains purchased from Jackson Laboratories, ranging in age from 8 to 12 weeks and weighing 18-30 g were used in all experiments. Mice were housed 8-10 per cage and Purina laboratory chow and water were available ad lib. &ne marrow counts. Mice were killed by cervical dislocation. After the humerus was removed and freed of soft tissue attachments, the epiphyseal cap was detached from the proximal end and the extreme distal tip of each epicondyle (less than 1 mm) was cut off. A 26-gauge needle with an epidermal bevel was inserted into the proximal end of the humerus and to it was attached a syringe containing 5 ml (measured in a volumetric pipette) of a solution of 1% ethylenediaminetetraacetate (EDTA) in 0.97’) 1 r sa ine. The solution was forced through the humerus, with the needle positioned in such a manner that fluid flowed freely from both ends of the bone. The cell washout was collected in a vial. The humerus, still mounted on the needle, was immersed in the fluid and approximately 2.5 ml was aspirated back through the humerus and then forced back through the bone into the vial. This was repeated until a total of approximately 15 ml of fluid was passed through the humerus-The cell