the body in two ways. (a.) Because it is a heat-producer-that is, being composed chiefly of carbon and hydrogen, it combines with oxygen to form carbonic acid and water, thus contributing to the heat of the body. (b.) Because it is a bad conductor of heat, and so helps to retain the warmth within the body. (2.) It is a packing material, filling up inequalities and forming a bed in which other structures can lie. (3.) It is protective, being deposited around and between different organs, affording them support, facilitating motion, and protecting them from the injurious effects of pressure. As examples of this last use may be mentioned the existence of fat in the palms of the hands and soles of the feet, in the orbits, and around the kidneys. When the digestive process introduces into the system more carbon and hydrogen than is required for immediate consumption, the excess of these elements is stored up in the form of fat, to be reabsorbed when required. The use of fat in nutrition is well illustrated in hybernating animals. Though the chief source of fat in the body is the oleaginous constituents of the food, it is also formed by the decomposition of saccharine and albuminous principles, which yield fatty acids, and, combining probably with glycerine, are converted into fat before their ultimate reduction into carbonic acid and water. Where found. I. Beneath the skin generally. 2. In the great omentum, mesentery, &c. 3. Lying on the outer surface of the synovial membranes, and filling up inequalities in joints. Absent from. 2. The penis. 4. The lungs. Fat tissue is also absent from the cranial cavity. As under normal conditions fat is decomposed into carbonic acid and water in the body, only minute quantities are met with in the healthy human excretions. Under abnormal conditions, however, fat appears in the excretions; when, for instance, the pancreatic and biliary ducts are occluded, the fats introduced with the food into the intestinal canal are not emulsified and saponified, and, remaining in consequence unabsorbed, pass unaltered out of the system with the fæces. In chyluria, also, fat globules are scen in the urine. CHAPTER III. Classification of Cartilage-Temporary Hyaline Cartilage-Articular, Costal, White and Yellow Fibrous Cartilages - Physical and Chemical composition of Cartilages - Chondrin, Gelatin, and Elastin contrasted. 7. CARTILAGE. 1. Temporary- B. Hyaline. 2. Permanent 1. Cellular (not present in man). 2. Hyaline (i.) Articular; (ii.) Costal. 3. Fibrous (a.) White fibro-cartilage— (i.) Interarticular; (ii.) Connecting; (iii.) Marginal; (iv.) Sesamoid. (b.) Yellow fibro-cartilage. I. TEMPORARY CARTILAGE. The term temporary cartilage is applied to that form of cartilage which exists in consider able quantity in the fœtus, and is subsequently converted into bone. Two varieties of it exist, the cellular and the hyaline. A. Cellular Cartilage is so called because, when examined under the microscope, it is seen to consist of numbers of small, more or less spherical, granular-looking cells, closely packed together. The matrix, which varies greatly in amount, consists of very fine fibres, which pervade the tissue throughout, passing between the cells in all directions, and enclosing them in a network. Cellular or, as it has been called, parenchymatous cartilage, is met with in the chorda dorsalis of the foetus, and it may also be readily obtained from the external ear of rats and mice. B. Hyaline Cartilage.-When a thin slice. of cartilage is examined under the microscope, it is seen to consist of nucleated cells imbedded in a solid matrix. Sometimes the matrix is dim and granular, like ground glass; while at other times it is clear and transparent. In hyaline cartilage, which is the typical form of the tissue, both these conditions occur. The cells of hyaline cartilage are masses of protoplasm, round or |