Celsus described the cardinal signs of inflammation as rubor, tumor, calor and dolor, which anyone who has suffered from a boil will recognize as redness, swelling, heat and pain. Galen added function laesa, or loss of function, the fifth cardinal sign. Stages of acute inflammation include vascular response, emigration of the white blood cells, and fluid exudates. Chronic inflammation occurs when the causative agent persists, i.e. it is not easily removed from the tissues. Microorganisms which are inadequately eliminated by the body defences cause a prolonged chronic inflammatory response. In some chronic inflammatory lesions, the repair process seems to be excessive, resulting in hyperplasia.