Why density of the fluid affect the capillary height?

Explain why is meniscus in capillary tube concave for water and convex for mercury.

Capillaries  Explain the direction and the rate of flow in the capillaries. Does the rate remain constant or does it fluctuate from time to time? Does the direction of blood flow ever change? What limits a capillary from being smaller than a certain size? Are any capillaries dead-end sacs? Are all cells directly adjacent to a capillary, thus providing a simple passage for food, dissolved gasses, and wastes?

If a fluid's speed increases, what happens with its pressure and how do you know?