The history of the knowledge of the phenomena of life and of the organized world can be divided into two main periods. For a long time anatomy, and particularly the anatomy of the human body, was the a and ? of scientific knowledge. Further progress only became possible with the discovery of the microscope. A long time had yet to pass until through the cell was established as the final biological unit. It would mean bringing coals to Newcastle were I to describe here the immeasurable progress which biology in all its branches owes to the introduction of this concept of the cell. For this concept is the axis around which the whole of the modem science of life revolves.