This, apart from the inherent interest Of the matter, must be my excuse for attempting an exhaustive statement, not only of the legislation and Of the parliamentary history, but also Of the scientific as well as Of the more ephemeral literature Of the topic, in the most important countries from which we have a lesson to learn. In this investigation, especially so far as England is concerned, virtually no help was secured from any existing investigation, and I have therefore been compelled to make a pioneer study, with all its inevitable defects. Some will no doubt take up this volume in the hope of securing a general survey Of the question. To such readers it is suggested that the main outlines Of the problem will be found in the Introduction and the Conclusion, and that they may do well to confine their attention to these portions of the work, referring to Parts I and II only in so far as they may be interested in securing a more detailed confirmation of the points there presented.