## **Core Concept**
The first internal sign of putrefaction refers to the earliest change that can be detected within the body during the decomposition process. Putrefaction involves a series of complex biochemical reactions primarily driven by the action of bacteria.

## **Why the Correct Answer is Right**
The greenish discoloration of the **liver** is considered the first internal sign of putrefaction. This change occurs due to the production of **sulphhemoglobin** and other gases by bacteria, which can diffuse through tissues and cause a greenish hue. The liver, being rich in blood and having a high bacterial load from the gut, is one of the first organs to exhibit such changes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While changes in the lungs can occur during putrefaction, they are not typically considered the first internal sign.
- **Option B:** The spleen does undergo changes during decomposition, but it is not the first organ to show internal signs of putrefaction.
- **Option C:** The kidneys can exhibit changes, but again, not the first internal sign.
- **Option D:** This option is not provided, implying we focus on why the other options are incorrect based on common knowledge.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that putrefaction can be influenced by several factors including environmental conditions (temperature, humidity), the presence of bacteria, and the condition of the body at the time of death. The greenish discoloration of the liver is an important forensic indicator of the early stages of decomposition.

## **Correct Answer:** . Greenish discoloration of the liver.