was generally quite unknown to them. The process by which ancient medicine usually attempted to find its hypothesis was by an argument from analogy. Each and every point of resemblance, however superficial, between two phenomena was considered sufficient by the ancient naturalists to warrant the assumption that analogous phenomena in the most various domains were most certainly proven to possess similar points of resemblance. And upon the basis of such an insecure method of deduction—which, moreover, was selected entirely at the option of the observer—the ancient investigator erected the boldest hypotheses. Thus, for instance, the atomic theory of Leucippus and Democritus is an hypothesis which rests upon the basis of a conclusion from analogy. The motes which appear in the rays of the sun led these two ancient investigators to the conception that, like the particles of dust sporting in the air, the primary component parts of everything that exists in the entire universe consisted of similar particles.[2] [2] Lucretius, Book 2, Verse 113, _sqq._ It appears that Epicurus arrived at his theory of light (according to which, as is well known, images of things were brought to the senses by delicate but absolutely objective small pictures which were detached from the surface of things in a continuous current) by the fact that many animals—for instance, snakes—shed their skins. The theory of humoral pathology, one of the most important advances in medical science, was based on a conclusion from analogy and arrived at by the deductive method. The diagnostico-theoretical lines in which antique medicine moved were bound—and this is the point of importance in this case—to exert a determining influence upon medical criticism. For medico-physical criticism can only appear in closest connection with the prevailing condition of the respective sciences, being really nothing else but a precipitate from them. Thus the ancient physicians were compelled to take an entirely different position toward magical medicine than we moderns, educated in the school of inductive methods, have always taken. The probable and similar, the supposable and possible, in which deductive medicine found its data, working on the lines of argument from analogy, were necessarily bound to find expression also in the character of medical critique, and it was impossible, therefore, for the ancient physician to detect anything absurd or contrary to experience in hypotheses which the practitioner of to-day at once brands as nonsensical and superstitious. We are not in the least justified, therefore, in speaking disparagingly of Galen and Alexander of Tralles because they believed in magical medicine and applied it in their practise. As no human being can jump out of his skin, so is he unable to get beyond the intellectual advancement of his time. As the ancient physicians were also unable to do this, accordingly they were believers in the magical medicine.