An eye is irritated when a spark from a locomotive, or a bit of sand, or an inverted eyelash, get into it. A mustard-plaster first stimulates the circulation of the skin where it is applied ; this may be quite within the bounds of healthy action, if the mustard be soon withdrawn. If it remain longer, irri-tation is shown by pain and soreness ; next, if still allowed to act, it. will produce inflam mation. Irritation of the stomach may be caused by indigestible food, or, more serious in degree, by certain poisonous substances ; as strong acids, alkalies, arsenic, or corrosive sublimate.