The law of innkeepers was the earliest developed and is the simplest and clearest of those topics of law which are con cerned with the various public-service callings. While its ex tent is slight, it is of considerable practical importance; and its theoretical interest is great to those who are concerned with the development and application of public-service law. It is the last aspect of the subject which drew the attention of the author to it. The practical importance and the legal interest of the public-service law justify a thorough study and investigation of it in all its applications. The rapid and enormous growth of the modern public-service corporations has outrun the law. The general principles by which they are governed have been apprehended by the courts, and the suc cess of the courts in applying these principles is a new triumph in our time for the plasticity of the common law; but these principles have not in all cases been formulated, after a care ful study of their origin and limitations, in a way which is entirely satisfactory and a careful study of them in all their applications seemed desirable.