In which of the following case, mice will remain alive in Griffith's transforming experiments ?

Options

A. Heat killed S - strain injected into mice .
B. DNA from heat killed S - strain + R - strain injected into mice .
C. S - strain injected into mice.
D. More than one option is correct

Answer

To determine in which case the mice will remain alive in Griffith's transforming experiments, we need to analyze the different scenarios presented in the question.

### Step-by-Step Solution:

1. **Understanding Griffith's Experiment**:
- Griffith worked with two strains of *Streptococcus pneumoniae*: the S strain (smooth, virulent) and the R strain (rough, non-virulent).
- The S strain has a polysaccharide coating that protects it from the host's immune system, while the R strain lacks this coating.

2. **Injecting Different Strains into Mice**:
- **Case A**: Injecting heat-killed S strain into mice.
- Result: Mice remain alive. (Heat-killed S strain cannot cause disease)
- **Case B**: Injecting DNA from heat-killed S strain plus live R strain into mice.
- Result: Mice die. (The DNA from the heat-killed S strain transforms the R strain into a virulent form)
- **Case C**: Injecting live S strain into mice.
- Result: Mice die. (Live S strain is virulent)
- **Case D**: More than one option is correct.
- This option is considered if multiple cases result in mice being alive.

3. **Conclusion**:
- From the analysis, we see that in Case A (heat-killed S strain), the mice remain alive.
- In Case B, the mice die due to transformation of R strain into virulent S strain.
- In Case C, the mice also die due to the presence of live S strain.
- Therefore, the only case where mice remain alive is Case A.

### Final Answer:
The mice will remain alive in Griffith's transforming experiments when injected with **A) heat-killed S strain**.

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