The finger or lobe of the ear is punctured as in making a blood count,
and the blood is allowed to drop directly into normal saline, ·85 per
cent. solution, containing about 1 per cent. sodium citrate; this
decalcifies the blood and prevents clotting. The corpuscles are
completely precipitated in the centrifuge, and then repeatedly washed
with ·85 per cent. saline and centrifugated, until all traces of the
citrate and serum are removed. After the final precipitation the saline
solution is withdrawn, and the thin upper grayish layer of the sediment,
the leucocytic cream, consisting for the most part of washed white blood
cells, is removed.