Nicholas Culpeper (probably born at Ockley, Surrey, 18 October 1616 - died at Spitalfields, London, 10 January 1654) was an English botanist, herbalist, physician, and astrologer. His published books includes The English Physitian (1652), i. e. the Complete Herbal (1653 ff), which contains a rich store of pharmaceutical and herbal knowledge, and Astrological Judgement of Diseases from the Decumbiture of the Sick (1655), which is one of the most detailed documents known on the practice of medical astrology in Early Modern Europe. Culpeper spent the greater part of his life in the English outdoors cataloguing hundreds of medicinal herbs. He criticized what he considered the unnatural methods of his contemporaries, writing: "This not being pleasing, and less profitable to me, I consulted with my two brothers, Dr. Reason and Dr. Experience, and took a voyage to visit my mother Nature, by whose advice, together with the help of Dr. Diligence, I at last obtained my desire; and, being warned by Mr. Honesty, a stranger in our days, to publish it to the world, I have done it."

Influenced during his apprenticeship by the radical preacher John Goodwin, who said no authority was above question, Culpeper became a radical republican and opposed the "closed shop" of medicine enforced by the censors of the College of Physicians. In his youth, Culpeper translated medical and herbal texts such as the 'London Pharmacopaeia' from the Latin for his master. It was during the political turmoil of the English civil war, when the College of Physicians was unable to enforce their ban on the publication of medical texts, that Culpeper deliberately chose to publish his translations in vernacular English as self-help medical guides for use by the poor who could not afford the medical help of expensive physicians. Follow-up publications included a manual on childbirth and his main work, 'The English Physician', which was deliberately sold very cheaply, eventually becoming available as far afield as colonial America. It has been in print continuously since the 17th century.  Culpeper believed medicine was a public asset rather than a commercial secret, and the prices physicians charged were far too expensive compared to the cheap and universal availability of nature's medicine. He felt the use of Latin and expensive fees charged by doctors, lawyers and priests worked to keep power and freedom from the general public.  Three kinds of people mainly disease the people - priests, physicians and lawyers - priests disease matters belonging to their souls, physicians disease matters belonging to their bodies, and lawyers disease matters belonging to their estate.  Culpeper was a radical in his time, angering his fellow physicians by condemning their greed, unwillingness to stray from Galen and their use of harmful practices such as toxic remedies and bloodletting. The Society of Apothecaries were similarly incensed by the fact that he suggested cheap herbal remedies as opposed to their expensive concoctions.

Answer the following question by taking a quote from the article: what was the closed shop of medicine?
the College of Physicians.