Explanation of Plate 1
From: Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types
The photograph was made by Mr. Joseph B. Haulenbeek.
Fig. 1. Colonies of the R variant (R36A) derived from Pneumococcus Type II. Plated on blood agar from a culture grown in serum broth in the absence of the transforming substance. × 3.5.
Fig. 2. Colonies on blood agar of the same cells after induction of transformation during growth in the same medium with the addition of active transforming principle isolated from Type III pneumococci. The smooth, glistening, mucoid colonies shown are characteristic of Pneumococcus Type III and readily distinguishable from the small, rough colonies of the parent R strain illustrated in Fig. 1. × 3.5.