HISTOLOGY, 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 histolo,gy treats of the tissues of man; compara tive histology treats of the tissues of the lower animals; and vegetable histolog-y treats of the tissues of plants. By oth ers histology is divided into three sec tions: general histology, which considers the tissues of which the human and ani mal body generally is composed; histol ogy proper, in which the various tissues in their anatomical relations and com position are considered; and topograph ical histology, dealing with the more minute structure of the organs and sys tems of the body. Each of these sub divisions may be divided again into nor mal histology, which refers to the healthy tissues, and pathological histol ogy, which investigates the changes they undergo in disease. Marie Francois Xa vier Bichat (1771-1802) is generally credited with the foundation of the sci ence of histology. The marvelous pow ers developed by the compound micro scope enable investigators now to pene trate into the most recondite tissues. It has been found that all structures how ever complex are made up of cells, and that the parts of a body may be re solved into a small number of elemen tary tissues now grouped as: (1) epi thelium, which lines almost all the cavr ties of the body and is directly or indi rectly in communication with the atmos phere; (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 blood-vessels and which take from the blood certain sub stances and secrete them; (5) connective substances, which support and hold to gether the more delicate and important structures, especially forming the carti leges and bones.
Many tissues have the power of re pairing injuries that happen to them. This power is called regeneration and is found especially in the lower animals, in polyps, worms, and in many amphibi ous creatures and reptiles. In other cases the lesion is supplied by a new growth of connective substance.
Vegetable histology is that department of botany which deals with the micro scopic phytotomy or anatomy of plants, especially investigating the plant cells and plant tissues.