Frederick Griffith · Transformation
Can a dead microbe change a living one?
That time, that place
Even after the 1918 influenza had passed, pneumonia remained a leading cause of death. Griffith was a physician in Britain's health ministry, studying pneumococcus in the hope of a vaccine.
The bacterium came in two forms. The smooth type wears a capsule, evades the body's defences, and kills mice. The rough type has no capsule, is eaten, and harms nothing. Each bred true, generation after generation.
Why this question
The experiment had four arms. Living rough type into a mouse: nothing. Living smooth type: the mouse dies. Heat-killed smooth type: nothing. So far, as expected.
One arm remained. Killed smooth type together with living rough type — two things that separately do no harm at all.
The mouse died.
What was found
From the dead mouse came living smooth-type bacteria — and their descendants stayed smooth. A change made once had held across generations.
Something inside the dead bacteria had crossed into the living ones and permanently made them a different kind. Griffith called it the transforming principle.
What it was, he did not know. He was not a student of heredity. Chasing a vaccine, he had arrived at the door of genetics without much sense that he was standing at one.
He died in his laboratory during the London Blitz in 1941.
A bacterium's kind is fixed, and the dead can do nothing to the living
Mice dying only from the two harmless things combined, and true-breeding smooth type recovered from the bodies
The hunt for that something led, sixteen years later, to Avery's experiment