Serum tellurite agar,1 which is used as a routine in this laboratory for the examination of cultures taken from the throat and nose for Corynebacterium diphtheriae, has been found very satisfactory for the isolation of pneumococci.
On this medium practically all strains of pneumococci produce very characteristic colonies. The colonies, which vary in size from 0.1 to 1 mm. in diameter, are very thin and flat, entire and gray with a brownish gray center. Some give the appearance of having a raised edge and a depressed center. Recently isolated and virulent type III pneumococci produced large (from 3 to 4 mm.), raised, watery, mucoid, light gray colonies. While the morphologic appearance of the colonies of pneumococci on this medium is very much like that produced on ordinary blood agar, the pneumococcus colonies are easily distinguished from those of streptococci. The colonies are not always typical, however, until the plates