White blood cells: because acupuncture penetrates the surface of the skin in what I like to call a “microsurgery”, it causes a small injury, alerting the body’s defenses and inducing the healing process to ensue. The body detects the needle penetration and sends white blood cells to the area to fight any possible infection, and when they find nothing wrong they go about cleaning up the area of any unnecessary stagnation that might be slowing the body down-scar tissue, excess fluid/edema, any old congealed blood, etc.