St. Luke, according to St. Paul, was a physician. When a physician writes a historical work it does not necessarily follow that his profession shows itself in his writing; yet it is only natural for one to look for traces of the author's medical profession in such a work. These traces may be of different kinds: 1, The whole character of the narrative may be determined by points of view, aims, and ideals which are more or less medical (disease and its treatment); 2, marked preference may be shown for stories concerning the healing of diseases, which stories may be given in great number and detail; 3, the language may be colored by the language of physicians (medical technical terms, metaphors of medical character, etc.). All these three groups of characteristic signs are found, as we shall see, in the historical work which bears the name of St. Luke. Here, however, it may be objected that the subject matter itself is responsible for these traits, so that their evidence is not decisive for the medical calling of the author. Jesus appeared as a great physician and healer. All the evangelists say this of Him; hence it is not surprising that one of them has set this phase of His ministry in the foreground, and has regarded it as the most important. Our evangelist need not therefore have been a physician, especially if he were a Greek, seeing that in those days Greeks with religious interests were disposed to regard religion mainly under the category of healing and salvation. This is true, yet such a combination of characteristic signs will compel us to believe that the author was a physician if, 4, the description of the particular cases of disease shows distinct traces of medical diagnosis and scientific knowledge; 5, if the language, even where questions of medicine or of healing are not touched upon, is colored by medical phraseology; and, 6, if in those passages where the author speaks as an eye-witness medical traits are especially and prominently apparent. These three kinds of tokens are also found in the historical work of our author. It is accordingly proved that it proceeds from the pen of a physician.