acid, and red by Millon's reagent, it is regarded as intermediate between syntonin and gelatin, some chemists assigning the formula C48 H38 N6 O16, or protein and 2 equivalents of water. Nothing is known of its development or reproduction. It possesses the valuable property of elasticity, which produces. force always antagonistic and secondary to muscular power. It is nearly as elastic as india-rubber, and regains this property on being moistened, although dried up for months. The ligamenta subflava, middle coat of arteries, vocal cords, crico-thyroid, thyro-hyoid, and stylo-hyoid ligaments, epiglottis, the tissue between the tracheal rings and the calceo-scaphoid ligament, which gives the spring to the foot, are examples of it. In quad rupeds the abdominal walls and the Yellow Elastic Tissue. ligamentum nucha, which supports the head of a grazing animal more constantly than muscles could, contain much of it. Areolar Tissue is the most universal of the constituents of the body. As the " superficial facia," it spreads under the skin, tying it to deeper parts, and giving a nidus for fat; it separates, yet connects muscles and other partshence named conjunctival by Henle; as the parenchyma, it constitutes the matrix of most solid or Areolar Tissue. gans; and, lastly, forms pads for the protection of, and smooth capsules for the free motion of such organs as the eye, which O'Ferrall has shown is enveloped in an exquisite structure he has named "tunica vaginalis oculi." When inflated and dried, this tissue is seen to consist of spaces freely communicating-hence the impropriety of the term "cellular," given to it by W. Hunter. Its areolæ permit the transmission of air (emphysema), serum, (anasarca), blood (ecchymosis), and other fluids, over a great extent of surface. It consists of threads of the white and yellow elements woven most inextricably together, but distinguishable by acetic acid, which exhibits nuclei in the former; and the tissue is generated by cells elongating, and joining in lines. Like both kinds of fibrous tissue, it is very slightly vascular, although many vessels pass through it en route to the skin; and any strangulation of them, as in anthax, will cause death of the latter. Its toughness, extensibility, and elasticity are admirably proportioned to mobility of each part-thus, it is loose and abundant in the axilla, orbit, and by the sides of the rectum; almost absent in firm glands-heart, brain, bone, or teeth; and most elastic about joints and the abdomen. Fat, the chemistry of which we have treated of already, is contained abundantly in the meshes of the areolar tissue. It is contained in cells from bo to do in diameter-spheroid if single, or polyhedral by mutual pressure. The cell-wall is extremely thin, and being moistened by serum, as Paget remarks, does not allow the fat to exude. Capillaries are looped round each cell. Adipose and areolar tissues are not always co-existent in equal amount; in canceli of bone, mesentery, Haversian masses, &c., we find fat with scarcely any areolar tissue, the reverse being the case in the eye-lids, about the penis, scrotum, Fat-cells surrounded by loops of Capillaries. ་ and bladder, and along the median line of the body. It seems to have no proper nerves or lymphatics. It is mechanically useful in padding exposed situations, its particles freely moving, and it obviates pressure, like a water cushion, and in retaining the heat within the body, for which reason it is most abundant externally in early life, and in aquatic mammals, as the whale, seal, &c. In old age and corpulent persons it heaps about the viscera, as the heart, liver, mesentery. It lessons the brittleness of the bones, and forms cushions in many joints. Its calorific office has been before considered. 66 Cartilage may be "temporary" and afterwards become bone; or permanent," which may be subdivided into "articular," covering the ends of bones, or "fibrocartilage," which builds up such organs as the external ear, nose, larynx, &c. Simple cartilage, as that which encrusts the end of any of the long bones, consists of oval cells with numerous granular nuclei, such as represented in the lower part of the next figure, embedded in a structureless matrix or hyaline substance. Prof. Beale regards this hyaline substance merely as the walls of the cells, proving the analogy between cartilage and such tissues as epithelium, which plainly are wholly cellular. The cells are often grouped in twos and threes, and are flatter towards the surface. It is covered by a delicate film of synovial epithelium, as demonstrated by Henle, especially in the foetus. This covering and the "circulus articuli vasculosus" of W. Hunter supply them freely with blood. It is of a pearly white colour, becoming yellow when dry. Fibro-cartilage is often membraniform, tough, elastic, and covered by a membrane, the perichondrium, which, like periosteum, conducts nutrient vessels. Inter-articular fibro-cartilages, in which the fibrous element abounds, are found in the following joints-knee, temporo-maxillary, sterno-clavicular, that between ulna and cuneiform, vertebræ and heads of ribs, and sometimes between acromion and clavicle. They are of a discoid or meniscoid shape, and afford a moveable and concave surface for the rounded bone. The glenoid and cotyloid ligaments surrounding the brim of the glenoid cavity and acetabulum, and the posterior tibio-fibular ligament, are of similar structure. As we shall find hereafter, the elastic laminæ of the cornea, capsule of lens, and zona pellucida of the ovum, present many analogies to the hyaline base of cartilage. The microscope has not yet detected vessels in cartilage large enough to carry the red cells; but in temporary cartilage, especially, there are vascular canals transmitting the plasma of the blood, and as the vessels of the synovial membrane and bone form many vascular loops in their immediate vicinity, we cannot call them "extra-vascular." Toynbee, however, states that cartilage is separated from bone by an impenetrable lamella. We owe all our knowledge of the pathology of the articular cartilages to the masterly investigations of Prof. Redfern, now of Queen's College, Belfast. The changes which occur in what is usually termed ulceration, but which is really a process of abnormal nutrition, he describes as follows: "They consist in the gradual enlargement and rounding of the cells which become filled with a mul Vertical Section of the Patellar Cartilage, showing the Cells, and the splitting of the hyaline mass at the surface when diseased, after Redfern. titude of corpuscles, which, on the bursting of the cells, are discharged into the texture, and removed from it by changes to be afterwards shown. The hyaline substance splits into bands and fibres, and is subsequently disintegrated and removed from the part." These two figures-selected, with his kind permission, from the great number which illustrate Prof. Redfern's work-exhibit the changes which occur. In the first, the splitting into fibres has taken place. In the second, the cells are as numerous as in temporary cartilage, and some have burst, leaving spaces in the hyaline substance. In many instances he has shown the "conversion of the nuclei into fatty granules and globules." We shall again allude to these most important discoveries when describing inflammation. Serous Sacs envelop all organs which move in performing their functions; and synovial membrane, which is of the same nature, surround bones where they are joined together, or lie about tendons where enter. The cavity is Multiplied and Enlarged Cells in Cartilage, filled with a halitus after Redfern. poured out by the membrane, and is closed-except in the |
