## **Core Concept**
The first internal sign of putrefaction refers to the earliest change that occurs within the body as a result of decomposition. Putrefaction is a process of microbial decomposition of organic matter, particularly proteins, in the body after death.

## **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, such as *Clostridium perfringens*, which are present in the gastrointestinal tract. These gases diffuse into the bloodstream and tissues, causing the characteristic greenish discoloration, which is first observed in the liver due to its proximity to the gut and its rich blood supply.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While changes in the lungs can occur during putrefaction, such as the presence of gas within the lung tissue, they are not considered the first internal sign.
- **Option B:** The spleen can become soft and congested during putrefaction but is not the site of the first internal sign.
- **Option D:** The kidneys may exhibit changes such as congestion and softening but are not the first internal site of putrefaction.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that putrefaction can be influenced by several factors including environmental temperature, presence of bacteria, and the body's own defense mechanisms. The greenish discoloration of the liver is an important early indicator of putrefaction and can be used in forensic pathology to estimate the post-mortem interval.

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