Fungus spores as uniform reference particles for use in absolute cell counts.

Spores of several different fungi were tested as microspheres in a recently described method of making absolute cell counts of bone-marrow cells. For a particular fungus to qualify for use in the counting method, it must be readily obtained and must produce large quantities of spores that are highly uniform in size. Thus far, the most satisfactory microspheres we prepared were the basidiospores of Calvatia gigantea, the giant puffball. This common field organism is a prolific spore producer. A simple procedure for obtaining spore suspensions was devised. Another source of microspheres is the conidia of species of Aspergillus and Penicillium. These widespread organisms were easily grown in the laboratory and also provided heavy spore harvests. It was suggested that conidia of these or additional species of fungi may be found useful in other kinds of research requiring small, highly uniform particles.