**Core Concept**
Vitreous preservation is a critical step in autopsy procedures, particularly for toxicology and forensic analysis. The vitreous humor, a clear gel-like substance in the eye, is rich in potassium ions and can provide valuable information about the deceased's metabolic state and potential exposure to toxins.

**Why the Correct Answer is Right**
The vitreous is preserved because it is less affected by post-mortem changes compared to other tissues, such as blood. This is due to the low water content and high potassium ion concentration in the vitreous, which makes it a more stable and reliable sample for analysis. Preserving the vitreous allows for the determination of the deceased's potassium levels, which can be indicative of the time of death and potential exposure to toxins.

**Why Each Wrong Option is Incorrect**
* **Option A:** Blood is not preserved for autopsy due to its susceptibility to post-mortem changes, such as bacterial growth and degradation of enzymes.
* **Option B:** Urine is not typically preserved for autopsy, as it can be contaminated with external substances and may not provide accurate information about the deceased's metabolic state.
* **Option C:** Tissue samples are often preserved for histopathological examination, but vitreous preservation is specifically for toxicology and forensic analysis.

**Clinical Pearl / High-Yield Fact**
The vitreous potassium concentration can be used to estimate the post-mortem interval (PMI) in cases where the exact time of death is unknown.

**Correct Answer:** B. Vitreous is preserved in a container filled with formalin or a similar preservative.