Paul Langerhans: a prilgrim "traveling" from functional histology to marine biology.

The nineteenth century was the time of a real revolution in science and medicine. A lot of seminal discoveries in medicine and biology were done in this time, and many of them were coincident with the introduction of the compound microscope by Hermann van Deijl and the standard histological technique by Paul Ehrlich. The main tissue types and individual cells were characterized and originally classified more than hundred years ago, although less attention was paid to their basic functions. This was mainly due to the modality of tissue specimen processing that allowed particularly detailed descriptive studies. Even so, we can notice some attempts to correlate the structure with the function. The German scientist Paul Langerhans, well-known for the discovery of Langerhans islets of the pancreas and Langerhans cells from the epidermis, tried to change the conventional fate of morphological studies introducing in his works functional hypothesis based on traditional microscopic observations even from the beginning of his scientific career. Paul Langerhans was a complex personality of the second half of the nineteenth century, not only in medicine, but also in other fields of biology. In the present review, presented is the life and research activity of Paul Langerhans, not only because of the importance of his discoveries, but also for perspectives that were opened by these findings in unexpected fields of medicine and biology.