Portrait painting benefitted greatly from such commissions and from the general appreciation of art by bourgeois clients, who supported portraiture as well as still-life and landscapes painting. In addition, the first significant art and dealer markets flourished in Holland at that time. With plenty of demand, Rembrandt was able to experiment with unconventional composition and technique, such as chiaroscuro. He demonstrated these innovations, pioneered by Italian masters such as Caravaggio, most notably in his famous "Night Watch" (1642). "The Anatomy Lesson of Dr. Tulp" (1632) is another fine example of Rembrandt's mastery of the group painting, in which he bathes the corpse
Nicolaes Tulp the condition we know as migraine, the devastating effects of tobacco smoking on the lungs, and reveals an understanding of human psychology in a description of the placebo effect. Tulp also discovered the ileocecal valve at the junction of the large and small intestines, still known as Tulp's valve. While Tulp made observations of various diseases, treatment often continued in the age-old way. His description of the symptoms of Beriberi in a Dutch seaman, for example, went unnoticed until the cause (vitamin B1 deficiency) was recognized two hundred years later by Christiaan Eijkman. Partially as a result of the success