[The medical illustration as the expression of illusion and imagination--the liver as an exampel from history].

The paper deals with concepts concerning the structure and function of the liver. According to the Hippocratic Collections the liver had five lobes. This concept was adopted by Galen and also became the concept of the medival physicians and teachers of anatomy. Still in his Tabulae Anatomicae from 1538, Andreas Vesalius illustrated the liver with five lobes, but in his public anatomy at Bologna in 1540 and in his famous books Fabrica and Epitome, both published in 1543, he stated that no such lobes existed in the human liver. The old wiew was based on animal dissections; thus in e.g. dog, cat, rabbit, swine and monkeys the liver has five or four distinct lobes. As a matter of fact the crucial question is not why, in a culture forbidding opening and dissection of human bodies, the on animals based concept, that the liver was split into five lobes, could arise and be maintained. The intriguing question is why the human liver still was said to have five lobes for more than 200 years after human autopsies had started. It is likely that the lag was partly due to belief in the ancient authorities and partly due to the fact that human anatomies were rare and most of the practical anatomy was still performed an animals. The role of the liver in the "physiological" thinkings of Plato, Aristotle, Herophilus, Erisitratus and Galen is also briefly touched. It is concluded that, with respect to physiology, the most important of Vesalius' contributions concerning the liver was not that he deprived the the human liver of its five lobes, but that he concluded in the Fabrica and Epitome that Galens concept of the liver as the source of the veins was wrong; the heart was the source of both veins and arteries. This concept had earlier been advocated by Aristotle and the agreement of Vesalius became a step towards the replacement of Galens physiology with the physiology of circulation of the aristotelian and brilliant experimenter William Harvey. A younger concept concerning the liver, which is based on findings in animals, but hardly relevant to man is the concept of lobules. This goes back to an eminent pioneer work on the liver of pig by F Kiernan in 1833. In this species there are distinct lobules, which everyone is completely invested by connective tissue. In man and many other mammals, however, the connective tissue is sparse and the lobular investment incomplete. The plates of hepatocytes form a continuum and the lobular structure is not fixed by a matrix of connective tissue but by dynamic factors as the pressure differance between the hepatic veins and the portal veins. Yet, still today, the liver lobule, although not present in man, always is presented in textbooks as the morphological and physiological unit of the liver.