An evaluation of the bone marrow, as cited previously, is typically accomplished by a cytologic examination of a Romanowsky type dyestained dry film smear of an aspirated sample of hemopoietic marrow. It is ideally performed with a prior morphologic evaluation of a concurrently obtained stained smear of the peripheral blood and a hemogram. Other biochemical data, sex, age, breeding status and life history of the subject can be of significant assistance in interpretation of the cellular picture of the sample. The estimation of the myeloid:erythroid ratio of the marrow, addressed in detail in an early segment of the text, is an integral part of the evaluation of the smear.