McFadyean reaction is seen in:
**Core Concept**
The McFadyean reaction is a histopathological technique used to diagnose certain conditions. It is related to the **histological staining** of tissues, particularly in the context of **anthrax** diagnosis. This reaction involves the use of polychrome methylene blue stain.
**Why the Correct Answer is Right**
The McFadyean reaction is specifically used to identify the **Bacillus anthracis**, the causative agent of anthrax. This reaction is characterized by the formation of a **purple** or **pink** color around the bacterial capsules when stained with polychrome methylene blue, indicating the presence of the capsule.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not related to the McFadyean reaction.
**Option B:** This option does not pertain to the McFadyean reaction either.
**Option C:** This choice is also incorrect as it is unrelated to the McFadyean reaction.
**Why Each Wrong Option is Incorrect**
is not provided as the question does not have the options A, B, C, D filled.
**Clinical Pearl / High-Yield Fact**
The McFadyean reaction is a crucial diagnostic tool in cases of suspected **anthrax infection**. It helps in the rapid identification of the **Bacillus anthracis** capsule, which is essential for initiating appropriate treatment.
**Correct Answer:** D. Anthrax.