It is not the author's desire to under value the literature Of the subject, but rather, acknowledging to the full its un doubted excellence, to endeavour to sup plement it by attempting to meet a demand which has been repeatedly made to him for a work which would be at once brief, com prehensive, and practical — a work which would rigorously omit what might prove burdensome or bewildering to the average reader; while, at the same time, it should give, in a simple and readable way, practical.