These men in particular may be remembered as the investigators who expanded the work of Bichat on the tissues: Schwann, for disclosing the microscopic elements of animal tissues and founding the cell-theory; Koelliker, as the typical histologist after the analysis of tissues into their elementary parts; Virchow, as extending the cell-idea to abnormal histology; Leydig, for applying histology to the lower animals; and Ramon y Cajal, for investigations into the histology of the nervous system. Text-Books of Histology.--Besides the works mentioned, the text-books of Frey, Stricker, Ranvier, Klein, Schäfer, and others represent a period in the general introduction of histology to students between 1859 and 1885. But these excellent text-books have been largely superseded by the more recent ones of Stöhr, Boem-Davidoff, Piersol, Szymonowicz, and others. The number of living investigators in histology is enormous; and their work in the subject of cell-structure and in the department of embryology now overlaps. In pathological histology may be observed an illustration of the application of biological studies to medicine. While no attempt is made to give an account of these practical applications, they are of too great importance to go unmentioned. Histological methods are in constant use in clinical diagnosis, as in blood counts, the study of inflammations, of the action of phagocytes, and of all manner of abnormal growths. In attempting to trace the beginning of a definite foundation for the work on the structure of tissues, we go back to Bichat rather than to Leeuwenhoek, as Richardson has proposed. Bichat was the first to give a scientific basis for histology founded on extensive observations, since all earlier observers gave only separated accounts of the structure of particular tissues. CHAPTER IX THE RISE OF PHYSIOLOGY Harvey Haller Johannes Müller Physiology had a parallel development with anatomy, but for convenience it will be considered separately. Anatomy shows us that animals and plants are wonderfully constructed, but after we understand their architecture and even their minute structure, the questions remain, What are all the organs and tissues for? and what takes place within the parts that are actually alive? Physiology attempts to answer questions of this nature. It stands, therefore, in contrast with anatomy, and is supplementary to it. The activities of living organisms are varied, and depend on life for their manifestations. These manifestations may be called vital activities. Physiology embraces a study of them all.