Histology

Collier's New Encyclopedia (1921)

that branch of anatomy which examines and treats of the minute structure of the tissues of which living organisms are composed. It is divided into several sections. Human histology treats of the tissues of man; comparative histology treats of the tissues of the lower animals; and vegetable histology treats of the tissues of plants. By others histology is divided into three sections: general histology, which considers the tissues of which the human and animal body generally is composed; histology proper, in which the various tissues in their anatomical relations and composition are considered; and topographical histology, dealing with the more minute structure of the organs and systems of the body. Each of these subdivisions may be divided again into normal histology, which refers to the healthy tissues, and pathological histology, which investigates the changes they undergo in disease. Marie François Xavier Bichat (1771-1802) is generally credited with the foundation of the science of histology. The marvelous powers developed by the compound microscope enable investigators now to penetrate into the most recondite tissues. 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 elementary tissues now grouped as: (1) epithelium, which lines almost all the cavities of the body and is directly or indirectly in communication with the atmosphere; (2) the nervous tissues, which as nerve cells originate and as nervous fibers 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 bloodwhich take from the blood certain substances and secrete them; (5) connective substances, which support and hold together the more delicate and important structures, especially forming the cartileges and bones. 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. Vegetable histology is that department botany which deals with the of microscopic phytotomy or anatomy of plants, especially investigating the plant cells and plant tissues.