Although herbalism had been part of medicine for millennia prior to the late 1800s, there were few truly effective chemical therapies. Real progress in pharmacology would depend on the later development of organic chemistry. However, prior to that, important shifts in thinking about chemical therapies began to occur in the Renaissance. The revival of Greek medicine at the end of the Dark Ages led to a revival and expansion of knowledge of herbal medicine and botany. Furthermore, as Europeans began to travel to Asia and the New World, they imported new plants and new medicines. Ultimately, this revival of herbal medicine led to organization and establishment of apothecaries, the forerunners of modern pharmacists. Paracelsus, who lived in the late 1400s and early 1500s, was a particularly important influence on early thinking about the role of chemistry in medicine. Paracelsus was the pseudonym of Swiss born physician Theophrastus Philippus Aureolus Bombastus von Hohenheim. His name Paracelsus was interpreted to mean that he surpassed Celsus, the Greek medical writer. Paracelsus briefly attended medical school in Italy, but he was largely informally educated. He rejected the dominant medical views of the time which were derived from Galenism. Indeed he wrote, "When I saw that nothing resulted from doctors practice but killing and laming, I determined to abandon such a miserable art and seek truth elsewhere." Paracelsus was a confusing figure in medical history. He rejected the medicine of the time when humorism, and he promoted the idea of disease as a real local entity. However, he subscribed to many fantastical and mythical views of health. His importance today however, is the champion new views of chemistry and chemical explanations of disease. Importantly, he believed that there were many kinds of disease and that each disease had a specific external cause. His fundamental conviction was that nature is sovereign and the healers responsibility is to know and obey nature. He championed observation and experimentation. Paracelsus argued that professors were blind to the truth, that only the pious common man could see the truth. He scoffed at writings and medical texts. He even told people to burn their books, sell their homes, to go travel, study plants, and learn from peasants. He came across as an angry man who antagonized many of those who he met, even those who tried to help him. Paracelsus theories of drug therapy primarily relied on metals and salts and opium. He championed a medicine of three principles, salt, sulfur, and mercury. He promoted use of compounds containing these chemicals. Although today, we would consider many of the treatments that he was prescribing at the time to be toxic or nonsensical, he at least at the time recognized the chemical treatments could lead to changes in health. He inspired a distinct school of medicine that stood in contrast to learned medicine in the universities of the time. He became favored by lesser ranks of healers, surgeons, apothecaries, and other irregular practitioners of medicine. He's still viewed as an influential figure in the development of alternative medicine and revered in some branches of alternative medicine today. Paracelsus's particular blend of medicine and chemistry became known as iatrochemistry. This approach to medicine became popular in Northern Europe. Whereas iatromathematics, medical mathematics, which was based on the careful measurement of bodily functions, was more popular in Southern Europe. Paracelsus was active and became influential during the time of the Protestant Reformation. Not surprisingly, his rejection of the dogmas of mainstream medicine of the time found a receptive audience and support among those who are similarly rejecting the authority of the Catholic Church. Not surprisingly, Paracelsus still remains a favored figure among alternative medicine practitioners today. Although most of Paracelsus's specific ideas about medicine were wrong and is proposed chemical remedies were worthless or even harmful, he was an important figure who weakened the hold of Galen's ideas on Western medicine and was one of the first promoters of the idea that chemical remedies could be used to treat specific illnesses.