**Core Concept**
Scurvy is a disease caused by a deficiency of vitamin C (ascorbic acid) in the diet, leading to impaired collagen synthesis, connective tissue weakness, and increased susceptibility to infections. It is a classic pediatric condition associated with a diet lacking in fruits and vegetables.

**Why the Correct Answer is Right**
The infant in this scenario is being fed cow's milk, which is deficient in vitamin C. As a result, the child develops symptoms of scurvy, including bleeding spots (petechiae), anemia, fever, and generalized tenderness. The swelling in the lower extremities is likely due to the breakdown of connective tissue, leading to edema. The normal blood count rules out other conditions such as leukemia or infections.

**Why Each Wrong Option is Incorrect**
**Option A:** Arthritis refers to inflammation of the joints, which is not the primary symptom in this case. While joint involvement can occur in scurvy, the infant's symptoms are more suggestive of a systemic condition.
**Option B:** Poliomyelitis is a viral infection that affects the nervous system, causing paralysis and muscle weakness. The symptoms described do not match polio, which typically presents with fever, muscle weakness, and paralysis.
**Option C:** Osteomyelitis is an infection of the bone, often caused by bacteria. While it can present with fever and swelling, the infant's symptoms and normal blood count make osteomyelitis less likely.

**Clinical Pearl / High-Yield Fact**
Scurvy can be prevented by ensuring infants receive a balanced diet that includes fruits and vegetables rich in vitamin C, such as strawberries, citrus fruits, and leafy greens.

**Correct Answer:**
✓ Correct Answer: D. Scurvy