"In the living man, there is an immaterial thinking substance, or MIND, constantly present; and every phenomenon of thinking is to be considered as an affection or faculty of the mind alone. But this immaterial and thinking part of man is so connected with the material and corporeal part of him, and particularly with the nervous system, that motions excited in this give occasion to thought; and thought, however occasioned, gives occasion to new motions in the nervous system. This mutual communication, or influence we affirm with confidence as a fact: But the mode of it we do not understand, nor pretend to explain; and therefore are not bound to obviate the difficulties that attend any of the suppositions which have been made concerning it."
William Cullen (1710-1790) was the leading British physician of the 18th century, and an important figure in the Scottish Enlightenment. He recognised the importance of the mind in healing, and was the first to describe the value of administering placebo treatments.
Cullen, as Professor of Chemistry first at the University of Glasgow and subsequently at the University of Edinburgh delivered one of the earliest courses of lectures on Chemistry; he introduced a system of chemical notation that was disseminated and published by several of his pupils. It has been said that Cullen was the first in Britain to acknowledge chemistry as an important, independent science, not just an appendage to medicine. His study of analytical chemistry was balanced by his sense that the patient’s ‘sympathetic constitution’ determined how he would respond to a prescribed therapeutic substance; he viewed almost all diseases as disorders of the nervous system, and coined the term "neurosis". He was an outstanding teacher, and his textbooks became very well known internationally. In his first year at Edinburgh University, his chemistry classes had just 17 students; eleven years later he had a class of 145. His influence extended far beyond Edinburgh: during his eleven years as Professor of Chemistry, he had forty American students, many of whom in turn sent their best students to Edinburgh. One was so inspired by Cullen that he named his son after him; William Cullen Bryant (1794-1878) became famous as the 'first American poet'. 
The economist Adam Smith was both a close friend and a patient, and his patients are known to have included the mathematician and philosopher Dugald Stewart. Cullen also had a lucrative mail-order practice; thousands of letters to him and copies of the advice he gave are held in the library of the Royal College of Physicians in Edinburgh 
Cullen, the son of a lawyer, was born in Hamilton, in Lanarkshire, Scotland on April 15th, 1710. After attending Hamilton Grammar School, he began a General Studies arts course at the University of Glasgow in 1726. He began his medical training as an apprentice to John Paisley, a Glasgow apothecary surgeon, then spent a year as a surgeon on a merchant vessel trading between London and the West Indies. After two years working as an assistant apothecary in London, he returned to Scotland to enter general medical practice in the parish of Shotts, Lanarkshire. From 1734 to 1736 he studied medicine at the University of Edinburgh, where he became interested in chemistry, and he was one of the founders of the Royal Medical Society. In 1736, he began medical practise in Hamilton, where he acquired a good reputation, and treated those too poor to pay without charge. In 1740, Glasgow University awarded him the degree of M.D.
In 1741, he married Anna Johnstone, the daughter of a minister, with whom he had seven sons and four daughters. He became ordinary medical attendant to the Duke of Hamilton, his family, and his livestock. In 1744, after the Duke's death, the Cullens moved to Glasgow. While working in private medical practise, Cullen continued to study the natural sciences, especially chemistry, and in 1747, he was awarded Britain's first independent lectureship in Chemistry and also was elected President of the Faculty of Physicians and Surgeons of Glasgow. In 1751, he was appointed Professor of the Practice of Medicine at the University of Glasgow, but continued to lecture on chemistry.
In 1755, Lord Kames persuaded him to move to the University of Edinburgh as Professor of Chemistry and Medicine. In 1756 he gave the first documented public demonstration of artificial refrigeration; he used a pump to create a partial vacuum over a container of diethyl ether, which then boiled, absorbing heat from the surroundings. From 1757 he delivered lectures on clinical medicine in the Edinburgh Royal Infirmary. When Charles Alston died in 1760, Cullen took over his course of lectures on Materia Medica; he delivered an entirely new course, the notes for which were eventually published as A Treatise on Materia Medica. HisMateria Medica was the first to use a Linnaean system of classification, providing a rational taxonomy of therapeutic substances. In 1766, he was appointed to the Chair of Institutes (theory) of Medicine at Edinburgh University and then became the sole Professor of Physic. In 1773 he was appointed as First Physician to the King in Scotland and elected President of the Royal College of Physicians in Edinburgh. In 1777 he was elected a Fellow of the Royal Society of London, and in 1783 he became a founding member of the Royal Society of Edinburgh.
His major published works were First Lines of the Practice of Physic; Institutions of Medicine (1710): and Synopsis Nosologiae Methodicae (1785), which classified diseases into four major classes (1) Pyrexiae, or febrile diseases, as typhus fever; (2) Neuroses, or nervous diseases, as epilepsy; (3) Cachexiae, or diseases resulting from bad habit of body, as scurvy; and (4) Locales, or local diseases, as cancer
A number of manuscript volumes of students' notes of Cullen's lectures are held in Scottish libraries; the contents of courses given at Glasgow in 1748-9 and at Edinburgh in 1757-85 have been examined in detail. The Edinburgh lectures covered general doctrines, on the laws of combination and separation, and the sources and modes of communication of heat and its effects on bodies, and particular doctrines, dealing with the five classes of bodies: salts, inflammables, waters, earths, and metals, with the properties of animal and vegetable substances, and concluding with the applications of chemistry in some of the practical arts such as agriculture, brewing, bleaching, and the manufacture of alkalis.
Cullen died on February 5th, 1790, at Kirknewton, near Edinburgh
- Institutions of Medicine: Part 1, Physiology by William Cullen (1785) (In 1772, while chair of the Institutions of Medicine at the University of Edinburgh, Cullen published this outline of physiology as a text-book. He divided his course into 3 parts: physiology, pathology, and therapeutics; texts for the other two parts were never published. - John Thomson (1859) An account of the life, lectures, and writings of Cullen Edinburgh, v. 1, p. 259, 432-433.)
- Kerr CE, Milne I, Kaptchuk TJ. William Cullen and a missing mind-body link in the early history of placebos
- Crellin, JK (1971), "William Cullen: his calibre as a teacher, and an unpublished introduction to his A Treatise of the Materia Medica, London, 1773", Med Hist 15: 79-87PMID 4929623
- Enlightenment evidence: William Cullen J R Coll Physicians Edinb 2009; 39:377
- William Cullen A Treatise of the Materia Medica
- The Works of William Cullen M.D. edited by John Thomson (1827)
- Wightman WPD (1955) Annals of Science 11:154-65
- William Cullen (1710-1790) by WP Boyd, The University of Edinburgh