These three Petri dish culture plates contained a casein-rich growth medium that had been inoculated from left to right, with Nocardia asteroides, N. brasiliensis, and a Streptomyces sp. organism. Note that the N. asteroides produced no hydrolysis reaction halo, while N. brasiliensis produced a minor reaction, and the Streptomyces sp. bacterium produced a strong hydrolytic reaction. Within the cleared halo region, casein had been hydrolyzed.