**Core Concept**
The question requires knowledge of the composition and function of the peri-lymphatic space, which surrounds the lymphatic vessels and nodes. Peri-lymph is a fluid that plays a crucial role in the maintenance of lymphatic vessel function and the regulation of lymphatic fluid dynamics.

**Why the Correct Answer is Right**
Peri-lymph contains a high concentration of electrolytes, proteins, and enzymes that help to regulate the permeability of lymphatic vessels and maintain the integrity of the lymphatic endothelium. The correct answer is **cholesterol**. Cholesterol is an important component of peri-lymph, and its presence helps to regulate the transport of lipids and lipoproteins across the lymphatic endothelium. This is essential for the proper functioning of the lymphatic system, including the transport of dietary lipids from the intestines to the bloodstream.

**Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because, although peri-lymph does contain proteins, the specific type of protein is not specified in the question.
* **Option B:** is incorrect because peri-lymph does not typically contain high concentrations of glucose.
* **Option C:** is incorrect because peri-lymph does not contain significant amounts of oxygen.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the composition of peri-lymph can vary depending on the location and function of the lymphatic vessel or node. For example, the peri-lymph of lymphatic vessels in the intestines may contain high concentrations of lipids, while the peri-lymph of lymphatic vessels in the skin may contain high concentrations of electrolytes.

**Correct Answer: C. Cholesterol.**