An article from Cassier's Magazine by H. M. Crawford on safety guards for self-acting spinning mules in cotton mills, mainly in Britain. It describes the parts that caused most accidents (headstocks, quadrant pinions, tightening pulleys, starting rods, back-shaft scrolls, drawbands and pulleys, carriage wheels, faller hammers) and the guards developed for each, with approximate costs, accident statistics and British regulations. It is illustrated with about 30 photographs of mules and guards.