HISTOLOGY (ante). Although Malpighi and Leuwenhoek, Busch, Lieberkiihn, and others, made several discoveries of minute parts with lenses, histology, as a science, did not commence until Bichat brought to bear upon the subject the powers of his generalizing mind, although his work was accomplished with but little aid from the microscope. Il is great work, entitled Anatomie generale apphgne a la Physiolagie et a la Medwine, appeared at Paris in 1801. He was the first to classify tissues to their structure. After Bichat came the epoch of histological research, the extension of the microscopic observations of M .
alnighi and Leuwenhoek accordance with the general system of Bichat. The discovery of the method of combining lenses so as to render them achromatic gave a new impulse to the study, and a more perfect i classification of the tissues of the body was the result, as it placed n the hands of i Schwann an instrument which, although a few errors were unavoidable in so new and profound a him to 'demonstrate the law that all tissues have their origin in cells. This may be called the greatest discovery in histology, and therefore Schwann is often called the founder of the science of histogenesis, or the study of the origin of tissues, more recently pursued with such great success by Reichert, Koelliker, Remak, and others. Then the microscopic anatomy of diseased structures and their mode of development came to be investigated, and the science of pathological histology took its rise. Johannes MtIller is regarded as the father of this branch of histology, as he indicated the general direction in which the investigation of diseased growths should be pursued. Afterwards Virehow, in the publication of his celebrated Cellular Yeticologjj, added new luster to the science, which has recently been still further enriched by the labors of BiIroth, Rindfleisch, Recklinghausen, Coluilienn, Now the science of histology enables the student to detect the elements of tissues in any organ, and also the first stages in the process of morbid growths by which the cell element gradually undergoes its transformation from a normal and healthy to an abnormal and sometimes malignant factor.
This brief historical notice needs only to be followed by a general view of those ele mentary tissues which it is the province of the science to investigate, and the study of whose functions forms so large a part of the science of physiology. In general terms, all tissues may be said to consist of cells, of one form or another. In cartilage the cells are globular or ellipsoidal, in the liver polygonal, in connective tissue long and spindle shaped. It was at first supposed that the elementary cell was composed of a little bag filled with fluid or solid matter, but now most histologists regard it as a small globular mass of living matter, or protoplasm, and this may have a nucleus, or exist without it. In regard to the power elementary cells may have of taking on different forms and becoming converted into different tissues, there is no certainty of knowledge. Whether the mature cells which form the various tissues have different natures in the first stages of their existence, or whether they are the results of transformations, cannot, perhaps, be determined; but it is more probable that each organ or tissue is made up of cells that are originally different; and it is by the development of this originally different organism, different not in form, perhaps, in any way that can be distinguished by the senses, but different in nature, that a primordial muscle cell will take to itself nutri ment from the blood plasma, and become in time a fully developed muscle cell, and, in connection with the nerves distributed to the part, perform its ordained functions; that a hepatic cell, existing at first as a blastimic point in the evolving organ, passes in the same way through the various stages of its development, till finally it becomes the mature hepatic cell, and never becomes anything else physiologically: it cannot change to any other tissue, unless it passes under the power of malignant disease, and turns to a cancer or a sarcoma cell, or degenerates from loss of vital power. Human tissue
elementary cells vary in size, from to ewer=s of an inch in diameter, of a inure or less ellipsoidal form, often nearly globular. There are two modes of cell growth, the endogenous, in which young cells form within the parent cell, and the exogenous. which takes place by a process of division; and this forms one of the grounds for believing that the cells of any tissue are always the cells of that particular tissue and no other. The most universal of all the elementary tissues of the body is connective tissue. As its name implies, it forms the connecting bond which holds together the special de ments of the several organs, passing between and around them. The cells which form the special part of each organ can generally be distinguished with the aid of the micro scope, varying widely in many instances, slightly iu others. The organs, however, con tain many tissues in common. They may in common have mucous membrane, but the cellular structure of this membrane differs in different organs. So far a special cellular element probably has the power of transformation, adapting itself to circum stances; but such transformation is different from that which would take place if an embryonic cartilage cell became an epithelial cell. Histology not only embraces the study of structural elements, but also elements of composition, or chemical elements, as well of the organs themselves as of their products. In this article no attempt can be made to do more than give an outline of what the science of histology is; the histo logical elements of many of the parts of the organs of the human body arc given under their appropriate titles. _Nothing has been said in this place of vegetable histology, although that science has existed longer, perhaps, than animal histology. and, being more simple, has been carried almost to perfection, while animal histology is scarcely out of its infancy; at least it is so immature that the results of its final development cannot be foretold.