It was an epoch in biological history when Vesalius overthrew the authority of Galen, and studied at first hand the organization of the human body. It was an epoch when William Harvey, by adding experiment to observation, demonstrated the circulation of the blood and created a new physiology. The two coördinate branches of biology were thus early outlined. The introduction of the microscope, mainly through the labors of Grew, Hooke, Malpighi, and Leeuwenhoek, opened a new world to the investigator, and the work of these men marks an epoch in the progress of independent inquiry. Linnæus, by introducing short descriptions and uniform names for animals and plants, greatly advanced the subject of natural history. Cuvier, by founding the school of comparative anatomy, so furthered the knowledge of the organization of animals that he created an epoch. Bichat, his great contemporary, created another by laying the foundation of our knowledge of the structure of animal tissues. Von Baer, by his studies of the development of animal life, supplied what was lacking in the work of Cuvier and Bichat and originated modern embryology. Haller, in the eighteenth, and Johannes Müller in the nineteenth century, so added to the ground work of Harvey that physiology was made an independent subject and was established on modern lines. With Buffon, Erasmus Darwin,, and Lamarck began an epoch in evolutionary thought which had its culminating point in the work of Charles Darwin. After Cuvier and Bichat came the establishing of the cell-theory, which created an epoch and influenced all further progress. Finally, through the discovery of protoplasm and the recognition that it is the seat of all vital activity, arrived the epoch which brought us to the threshold of the biology of the present day. Step by step naturalists have been led from the obvious and superficial facts about living organisms to the deep-lying basis of all vital manifestations. CHAPTER II VESALIUS AND THE OVERTHROW OF AUTHORITY IN SCIENCE Vesalius, although an anatomist, is to be recognized in a broad sense as one of the founders of biology. When one is attempting to investigate animal and plant life, not only must he become acquainted with the external appearance of living organisms, but also must acquire early a knowledge of their structure, without which other facts relating to their lives can not be disclosed. Anatomy, which is the science of the structure of organized beings, is therefore so fundamental that we find ourselves involved in tracing the history of its rise as one part of the story of biology. But it is not enough to know how animals and plants are constructed; we must also know something about the purpose of the structures and of the life that courses through them, and, accordingly, after considering the rise of anatomy, we must take a similar view of its counterpart, physiology.