**Core Concept**
Anaerobic bacterial infections can lead to the production of gas in subcutaneous tissues, a condition known as gas gangrene. This process is mediated by the action of Clostridium perfringens, a gram-positive, anaerobic bacterium.

**Why the Correct Answer is Right**
Gas gangrene is caused by the production of alpha toxin (phospholipase C) by Clostridium perfringens. Alpha toxin disrupts cell membranes, leading to the breakdown of cellular components and the production of gas. The gas is primarily composed of carbon dioxide and hydrogen, which accumulate in the subcutaneous tissues, causing swelling, pain, and tissue damage. The presence of gas in tissues can be detected clinically by crepitus, a grating or bubbling sensation under the skin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a bacterium associated with gas formation in subcutaneous tissues.
**Option B:** This option is incorrect because it does not mention the specific toxin involved in the pathogenesis of gas gangrene.
**Option C:** This option is incorrect because it does not accurately describe the composition of the gas produced in gas gangrene.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of gas gangrene is the presence of crepitus, which can be detected by gently palpating the affected area. This finding is often accompanied by severe pain, swelling, and tissue necrosis.

**Correct Answer: C. Clostridium perfringens**