a standard work and set an example for all the other cities of Holland. Rembrandt's painting The praelector would give yearly anatomy lessons each winter, performing them on victims of public hanging. At that time the dissection of bodies was only legal if the subject was a male criminal and considered outside of the Church. The dissections were performed with the consent of the city council and were a means to collect funds for city council meetings and dinners. All council and guild members were required to attend and pay an admission fee. Throughout Europe, these dissections were attended by prominent learned men, who exchanged ideas about anatomy and the chemical processes of the human body. As befits a new praelector, the Guild commissioned a new group portrait of the prominent councilmen and guild masters. Rembrandt, himself a young man of 26 and new to the city, won this commission and made a famous painting of him: The Anatomy Lesson of Dr Nicolaes Tulp. This painting, which now hangs in the Mauritshuis museum of the Hague, depicts Tulp dissecting such a criminal's forearm. There has been much speculation as to why the dissection began on the forearm. Rembrandt's event depicted in the painting can be dated to 16 January 1632; the Amsterdam Guild of Surgeons, of which Tulp was official City Anatomist, permitted only one public dissection a year and the body would have to be that of an executed criminal. The criminal is identified as the robber Aris Kindt. Rembrandt would later make a painting of Tulp's successor in 1656 The Anatomy Lesson of Dr. Jan Deijman. Since the painting of Tulp's predecessor in 1619, The Osteology Lesson of Dr. Sebastiaen Egbertsz was a group portrait around a skeleton, it is clear that the subject of a dead body had set a precedent. It would be another 100 years before the surgeons were allowed to dissect a female cadaver. "The Book of Monsters" His most impressive work on medicine was his Observationes Medicae, published in 1641 and again in 1652 by Lodewijk Elzevir. He wrote the first version for his son who had just graduated from Leiden and dedicated the second edition to him after his death. The book comprises minute descriptions of his work, including 231 cases of disease and death. Some called it the "book of monsters" because Tulp dissected animals brought back from the Dutch East