DNA (Role in Inheritance) — Overview & Importance

Frederick Griffith was a scientist who experimented with certain bacteria and their effect on mice. He found that a disease-causing strain of bacteria killed the mice, while a harmless strain did not. He then killed the disease-causing bacteria with heat and found that these no longer had an effect on the mice. However, when he mixed the heat-killed bacteria with harmless bacteria the mice died.

What did Griffith call the ability of the heat-killed bacteria to somehow change the harmless bacteria into disease-causing ones?