Regarding, in the first place, internal medicinal treatment, the astrologer knew how to give positive information about the same; for all terrestrial beings, of an organic as well as of an inorganic nature, were under the influence of the sun, the moon, of the planets, and of the signs of the zodiac. The stars imparted certain powers to the planets, to animals, and to all structures of the inorganic world. If, therefore, it were known what stars happened to appear in the vault of heaven at the beginning of the disease or of its treatment, it was only necessary seriously to consider the organic and inorganic structures under their supervision, and the remedies required for a successful control of the disease were presently at hand. But if the healer wished to be absolutely certain what medicaments to choose, the phases of the moon and the condition of the sun were also to be taken into consideration. Some remedies could be administered only when the moon was in a particular relation to certain planets or stars of the zodiac. These remedies were principally emetics and purges. Similarly to the internal clinician, so also in surgery, the healer was entirely dependent upon the conjunction of the stars. The primeval Babylonian directed that the body must not be touched with iron during certain conjunctions of the stars, and this was also prescribed in all cases of _Astrologica Medica_. It appears, however, that this direction obtained less general surgical recognition, but referred principally to blood-letting. Even to this limited extent it implied a high-handed interference with the art of the ancient as well as of the medieval physician; for venesection occupied an entirely different position among therapeutic measures during that period than it does to-day. Whereas modern medicine does not consider blood-letting necessary, except in the rarest cases, ancient as well as medieval professors of medicine believed that they could under no circumstances dispense with it; in fact, it is probable that until the seventeenth century there was scarcely any form of disease the treatment of which would have been possible without withdrawal of blood. An actual system of blood-letting had been elaborated under the influence of humoro-pathological opinions. Every vein that could be reached with the lancet was acted upon, and the school of medicine of the period was punctiliously careful in teaching which vessel presented the most suitable point of attack for the hand of the physician in this or that form of disease. The therapeutic subtleties which were thus brought to light are beyond description. Thus, a withdrawal of blood from veins on the right side of the body was said to yield an essentially different effect from left-sided venesection, and each individual vein of the body promised a special advantage which was peculiar to this one vein. The physician of that period surely had enough to do to bear in mind