Griffin worked on a project that enabled others to point out that DNA was the molecule of inheritance. Griffith's experiment involved mice and two types of pneumonia, a virulent and a non-virulent kind. He injected the virulent pneumonia into a mouse and the mouse died. Next he injected the non-virulent pneumonia into a mouse and the mouse continued to live. After this, he heated up the virulent disease to kill it and then injected it into a mouse. The mouse lived on. Last he injected non-virulent pneumonia and virulent pneumonia, that had been heated and killed, into a mouse. This mouse died.
Why? Griffith thought that the killed virulent bacteria had passed on a characteristic to the non-virulent one to make it virulent. He thought that this characteristic was in the inheritance molecule. This passing on of the inheritance molecule was what he called transformation.
