The remaining instrument of progress is the law schools. “Legal education,” says Bryce, “is probably nowhere so thorough as in the United States.” The chief reasons for this success are two, the professional law teacher, who has replaced the retired judge and the practising lawyer who lectured in his spare hours; and the case-system of instruction. This method is not, as is popularly believed, the memorization by the students of the facts of innumerable cases. It imparts legal principles, not on the say-so of a text-book or a professor, but by study and discussion of the actual sources of those principles, the decisions of the courts. The same method in the Continental Law would result in a class-room discussion of codes and commentators, which are there the sources. One of the most interesting signs of its success is its spread from law into other sciences such as medicine. Books based on the study of concrete situations are used in public schools for the study of geography and hygiene, and charitable societies work out the general needs of the community from the problems of individual families. This system has superseded in all the leading law schools the old methods of lecturing and reading treatises. Its most conspicuous service is, of course, vocational, the training of men whose advice a client can safely accept. Already some States have required a law-school degree as a condition of admission to the bar, and the old haphazard law-office apprenticeship will eventually disappear, although the question of how far a man who is earning his living should be allowed to study law in his spare hours at a night law school whose standards must usually be lower than a full-time school remains as a difficult problem in a democratic country. Efficiency of training conflicts with equality of opportunity. A second service of the leading law schools is the modernization of the law through the production of books. A great example of this is the “Treatise on Evidence,” by John H. Wigmore, dean of Northwestern Law School, which is every day influencing courts and renovating the most antiquated portion of the common law.