"In the second century, the _Galenic System_ was founded by Claudius Galenus. This might, indeed, only be considered the revival of the dogmatic or Hippocratean system. Galen professed to have selected what he found valuable from all the prevailing systems, and has embraced the elements and ruling spirit of the pneumatic school. Thus he explained the operation of medicines by reference to their elementary qualities,--that is, heat, cold, dryness, and moisture,--of each of which he admitted four degrees. But he was governed by a prevailing partiality for the system of Hippocrates, which, he states, was either misunderstood or misrepresented by all theorists, ever since the establishment of the empiric and methodic schools. He devoted most of his time to commenting upon and embellishing it, and thus again established a system, founded on reason, observation, and sound induction, which maintained its character, without a rival, for more than one thousand five hundred years. "Near the middle of the sixteenth century, Paracelsus introduced the _Chemical System_. This was strongly opposed by Bellonius and Riverius, who maintained the doctrine of Hippocrates and Galen. But the presumptuous Paracelsus burned, 'in solemn state,' the works of the ancients; and being succeeded by the indefatigable Van Helmont, the whole science of medicine was overwhelmed by the mysticism of the alchemical doctrines and languages. The chemical theory, in the main, rejects the influence, or even the existence, of the _vis medicatrix naturæ_, and explains all physiological, pathological, and therapeutic operations upon abstract chemical laws. Thus chemical or inorganic agents, and many of the most virulent poisons, as arsenic, mercury, antimony, &c., were placed among the most prominent remedies. "Soon after the introduction of the chemical system, medical science, if we make one exception, became less eccentric, but much less marked for the permanency of its systems. Boerhaave ingeniously blended most of the prominent doctrines of the Galenic and chemical systems; and by an application of several of the newly-developed natural sciences, especially mathematics and natural philosophy, he led his successors into a more even path and fixed method of investigation; for no more do we find any abstract physical laws the sole basis of a system. But these were the highest honors allowed Boerhaave; his particular system was soon subverted by Stahl, who proved the supreme superintendence of an immaterial, vital principle, corresponding to that pointed out by Hippocrates. To this he ascribes intelligence, if not moral attributes. Hoffman led Cullen into the path that brought him into the fruitful field of _nervous pathology_ and solidism, which, with a modification of Stahl's ruling _immaterial essence_, formed the groundwork of his admired system.