**Core Concept**
The demonstration of old washed-up blood-stains involves a technique that utilizes the properties of hemoglobin to visualize and identify bloodstains that have been subjected to water washing or other forms of degradation. This method is essential in forensic science and pathology for analyzing and interpreting bloodstains found at crime scenes or on clothing.

**Why the Correct Answer is Right**
The correct answer involves the use of **Hematoxylin and Eosin (H&E) stain** or **Luminal** to demonstrate old washed-up blood-stains. The H&E stain is a widely used histological technique that can help visualize the presence of hemoglobin in bloodstains, even after they have been exposed to water or other substances. Luminal, on the other hand, is a fluorescent dye that can bind to the heme group of hemoglobin, allowing for the visualization of old bloodstains under ultraviolet (UV) light. This technique is particularly useful in forensic science for analyzing bloodstains that have been degraded or washed away.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **Giemsa stain** is typically used for staining parasites and certain types of bacteria, not for demonstrating old blood-stains.
**Option B:** This option is incorrect because **Methylene blue** is a general-purpose stain used for various applications, but it is not specifically used for demonstrating old blood-stains.
**Option C:** This option is incorrect because **Crystal violet** is a stain used for Gram staining and other applications, but it is not used for demonstrating old blood-stains.

**Clinical Pearl / High-Yield Fact**
In forensic science, the ability to demonstrate old blood-stains is crucial for analyzing and interpreting evidence. The use of H&E stain or Luminal can help investigators and forensic scientists reconstruct crime scenes and identify potential suspects.

**Correct Answer: C. Luminal**