Griffith's experiment has 4 phases:

1. Phase 1: Disease causing bacteria named 'S' strain injected in the mouse, kills it.
2. Phase 2: Harmless bacteria named 'R' strain is injected in a mouse and has no effect on it.
3. Phase 3: Heat killed bacteria of S strain is injected in a mouse and has no effect on it.
4. Phase 4: Mixture of heat-killed S strain and live R strain is injected in the mouse killing it. Here live S strain is isolated from this mouse.