Not only is a person liable for those injuries which he personally commits, but, under certain conditions, he may also be liable for injuries inflicted by agencies or instrumentalities under his control. The three important classes of such agencies or instrumentalities are (1) human agents; (2) animals; (3) inanimate dangerous agents, such as fire, explosives, and artificial accumulations of water.1 The first of these has been already considered under the subject of Agency;2 the two latter will be taken up in the present chapter.