In the 1920s, bacteriologist fred griffith demonstrated that a heat-killed, infectious pneumococcus produced a substance that could convert a harmless form of the bacterium into a lethal one. fifteen years later, researchers prepared an extract from the disease-causing s-strain pneumococci and showed that this material could transform the harmless r-strain cells into the infectious s-strain form. this change to the bacteria was both permanent and heritable, suggesting that this "transforming principle" represents the elusive genetic material of the cells. but what kind of molecule was it? the researchers subjected their extract to a variety of tests to determine the chemical identity of the "transforming principle." in one experiment, they treated the material with enzymes that destroy all proteins. this treatment did not affect the ability of the extract to transform harmless bacteria into an infectious form. from this result, the researchers can conclude that: