**Question:** Whitehead's varnish in gauze is used to arrest bleeding from:

A. Vascular lesions
B. Hemostatic agents
C. Non-vascular lesions
D. Gastrointestinal bleeding

**Correct Answer:** C. Non-vascular lesions

**Core Concept:** Whitehead's varnish is a hemostatic agent used to stop bleeding from various sources, particularly in dermatology and plastic surgery. In the context of this question, we'll focus on its application in arresting bleeding from non-vascular lesions.

**Why the Correct Answer is Right:** Whitehead's varnish, also known as gauze impregnated with a mixture of iodine, potassium iodide, and glycerin, acts as a hemostatic agent by:

1. Increasing vascular permeability: The iodine and potassium iodide components enhance vascular permeability, allowing blood to extravasate into the surrounding tissue, increasing blood vessel congestion and pressure, thus promoting hemostasis.
2. Providing a physical barrier: The glycerin-impregnated gauze serves as a mechanical barrier, preventing further blood loss while the vessel constricts and clots form.

**Why Each Wrong Option is Incorrect:**

A. Vascular lesions: Although Whitehead's varnish can be used in certain cases to control bleeding from small vessels, it is not specifically designed or effective for large vessels, making this option incorrect.

B. Hemostatic agents: This option is incorrect as Whitehead's varnish is not a standard hemostatic agent but rather a specific method using a mixture of iodine, potassium iodide, and glycerin.

D. Gastrointestinal bleeding: Whitehead's varnish is primarily used for skin and mucous membrane bleeding, not for managing internal bleeding.

**Clinical Pearl:** Whitehead's varnish is commonly used in dermatology and plastic surgery to control minor bleeding from skin and mucous membrane lesions. It is effective particularly in cases where other hemostatic agents are not available or contraindicated.