Griffith

• Griffith's Experiment:

  1. living encapsulated bacteria injected into mouse : mouse died.
  2. living nonencapsulated bacteria injected into mouse : mouse remained healty
  3. heat-killed encapsulated bacteria injected into mouse : mouse remained healthy
  4. living nonencapsulated and heat-killed encapsulated bacteria injected into mouse : mouse died
• Griffith's first step was to inject a mouse with living encapsulated bacteria. The mouse died because the virulant bacteria was unable to be digested by its immune system.
• Griffith's second step was to inject a mouse with living nonencapsulated bacteria. The mouse remained healthy because the non-virulant R-strain of pneumonia bacteria was digested by its immune system.
• Griffith's third step was to inject a mouse with heat-killed encapsulated bacteria. The mouse remained healthy because the heat-killed pathogenic S-strain was denatured.
• Griffith's fourth step was to inject a mouse with living nonencapsulated and heat-killed encapsulated bacteria. The mouse died because the non-virulant R-strain picked up genes from the heat-killed S-strain which transformed it into the pathogenic S-strain (the transformation principle).