HISTOLOGY, the science of animal and vegetable tissues. It investigates by means of the microscope the various tissues of man, ani mals and plants in their anatomical relations and compositions. Topographical histology considers the more minute structures of the organs and systems of the body; normal his tology deals with the healthy tissues; and pathological histology investigates the changes they undergo in disease. Marie Francois Xavier Bichat (1771-1802) is generally credited with the foundation of the science of histology. Un fotunately the imperfect condition of the microscope in his time prevented Bichat and his contemporaries from carrying their investiga tions to the point which Schleiden, Schwann, Johann Midler, Virchow, Von Recklinghausen, Cohnheim, etc., have reached. It has been found that all structures however complex are made up of cells, and that the parts of a body may be resolved into a small number of ele mentary tissues now grouped as: (1) epithel ium, which lines almost all the cavities of the body and is directly or indirectly in communi cation with the atmosphere; (2) the nervous tissues, which as nerve cells originate and as nervous fibres transmit all nervous impulses; (3) muscle, which produces motion whether voluntary or involuntary; (4) glandular tissue which consists of cells standing in close relation with the blood-vessels which take from the blood certain substances and secrete them; (5) connective substances which support and hold together the more delicate and important struc tures, especially forming the cartilages and bones. See PLANTS, STRUCTURE OF.
Many tissues have the power of repairing injuries that happen to them. This power is called regeneration, and is found especially in the lower animals, in polyps, worms and in many amphibious creatures and reptiles. In other cases the lesion is supplied by a new growth of connective substance. In diseases
the tissues undergo many changes and many of these diseases in the organism are shown also by the changing of color. The science of such changes is is called pathological his tology. It s a comparatively young science and has been cultivated by Virchow, who was the founder of cellular pathology.
Vegetable histology is that department of botany which deals with microscopic phytotomy or the anatomy of plants, especially investigat ing the plant cells and plant tissues. It is prop erly subordinate to morphology and is a dis tinctively descriptive science. It deals with the question in what relation the cells or forms of tissue stand to the vital activity of plants, what functions they perform, and in what respect they are constituted for the fulfilling of those functions. (Compare CrroLocv). Owing to the excessive minuteness of the cells which form the tissues of all plants the investigation relies almost entirely on the microscope, and naturally has made its advance in proportion as the microscope has been made more perfect. Microscopes that are now used magnify at least 1,000 diameters, and the materials used have to be carefully prepared and mounted. Many of them have to be colored with hrinatoxylin, fuchsin, saffranin, and other alcoholic or aqueous dyes. Consult Bailey, F. R., of Histology' (4th ed., New York 1913) • Chamberlain, C. J., 'Methods in Plant Histology' (2d ed., Chicago 1905) • Lee, A. B., Vade-mecum' (6th ed., Philadelphia 1905) •, Strasburger, E., book of Practical Botany' (7th ed., New York 1911) ; Delafield and Prudden, (Handbook of Pathological Anatomy and Histology) (9th ed., New York 1911).