But Paracelsus was a chemist, and the terrestrial nature of man was his peculiar interest. The theologian may prescribe for the human soul, and it is the duty of the astronomer to care for the human intellect; but the practical physician must understand the human body. Here is the Archæus imprisoned in the gross terrestrial body! It is in continual warfare with that body. What is the nature of that body which is so hostile to the human vital principle? Here Paracelsus introduces his strange chemical analysis which characterizes him as a Renaissance physician. Nature has three essences of which all bodies are composed: (1) mercury, that makes bodies liquid; (2) sulphur, that makes them combustible; (3) salt, that makes them rigid. These essences are compounded in such a way that from them the four elements――earth, air, water, and fire――are derived. Each one of these elements is controlled by elemental spirits. The earth is controlled by gnomes, the water by undines, the air by sylphs, and the fire by salamanders. Thus the chemical analysis of Paracelsus discovers four sets of spirits with which the physician is obliged to deal. Gnomes, sylphs, undines, and salamanders are in warfare with the human vital principle for control. When the Archæus is in any way checked by these, there is disease; when the Archæus has them under control, the man has health. The medicines that the physician administers are determined by their effectiveness in helping the Archæus in its battle against the hostile spirits. This makes medicine a field for the magician in the control of spirits. =Giordano Bruno= (1548–1600). The neo-Platonic spirit of the Humanistic Period reached its most complete development in the æsthetic philosophy of Giordano Bruno. He sang the world-joy of the æsthetic Renaissance. Italy ordained him priest, exiled him as heretic, and then burned him at the stake as recalcitrant. Italy has produced very few great speculators since his day. The Council of Trent met when he was fifteen years old; already the counter-Reformation had begun in Italy, and Italy was soon to become an intellectually arid waste. The influence of Bruno appears in Spinoza and perhaps in Leibnitz. His one contribution to modern science was in his inspired conception that because God is infinite, the world is infinite in space and time. The philosophers who influenced his thought were Pythagoras, Plato, Plotinus, and Lucretius.