In the late 1920s, bacteriologist Fred Griffith was studying Streptococcus pneumoniae. This bacterium comes in two forms: one that is highly infectious (called the "S strain" because it forms colonies that appear smooth when grown on a nutrient plate in the lab) and one that is relatively harmless (called the "R strain" because its colonies appear rough). When injected into mice, the S strain is lethal, whereas the R strain causes no ill effect. Griffith confirmed that when the S strain is killed by heating, it is no longer infectious. But he then discovered that if he injected mice with both the heat-killed S strain pneumococci and the live, harmless R strain bacteria, the animals died of pneumonia. Furthermore, their blood was swarming with live, S strain bacteria that, when grown in culture, remained infectious and lethal.

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Social Studies

Allie Cobb

23 May, 20:34

In the late 1920s, bacteriologist Fred Griffith was studying Streptococcus pneumoniae. This bacterium comes in two forms: one that is highly infectious (called the "S strain" because it forms colonies that appear smooth when grown on a nutrient plate in the lab) and one that is relatively harmless (called the "R strain" because its colonies appear rough). When injected into mice, the S strain is lethal, whereas the R strain causes no ill effect. Griffith confirmed that when the S strain is killed by heating, it is no longer infectious. But he then discovered that if he injected mice with both the heat-killed S strain pneumococci and the live, harmless R strain bacteria, the animals died of pneumonia. Furthermore, their blood was swarming with live, S strain bacteria that, when grown in culture, remained infectious and lethal.

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Tatiana Johnston · Answer 1

It can be inferred that certain substances that are in the infectious S strain could transform the harmless R strain into the more dangerous form

Explanation:

Based on the research studies and the discovery of the bacteriologist, it was discovered that there are certain chemicals or substances in the S strain. These chemicals could alter the composition of the harmless R strain. It could also lead to the formation of the dangerous form of the chemical from the less harmful and harmless R strain.