Bichat made 21 distinctions of animal texture, but later anatomists have modified his method of distinction. It will suffice here to say that the sheath or covering membranes of bones, muscles, nerves, and many other organs, are formed of a fibrous kind of membrane, much alike in texture and in its leading properties, whether it be the periosteum of the bones, the fibrous sheath of the muscles, the neurilemma of the nerves, or the tunica albuginea or covering of the testicles, the ovaries, etc Serous membrane is also the same kind of tissue in every part of the body, although called arachnoid when it serves as a covering for the brain, pleura as a covering for the lungs, and peritoneum as a covering for the viscera of the abdomen, and a lining for the inner walls of the trunk below the chest. The leading elements of structure in the organs of the body are fibrous tissue, serous membrane, bony texture, cartilaginous texture, fibro-cartilage, muscular fibre of various kinds, striated and non-striated, glandular tissue, mucous membrane, dermoid tissue or skin, cuticle or epidermic tissue on the surface of skin and mucous membrane, horny tissue, as the hair and nails, white nervous or medullary substance, and gray nervous or ganglionic or vesicular matter; and diseases are characterized in many instances, not so much by the particular organ affected in any part of the body, as by the particular tissue affected by disease in any given region. - Minute anatomy goes deeper still into details, and with the microscope and chemical analysis endeavors to find out the elementary constitution of the tissues and fluids of the body.

Thus chemistry reveals to us that the simple elements found in the tissues are oxygen, carbon, hydrogen, nitrogen, sulphur, phosphorus, magnesium, calcium, sodium, potassium, chlorine, fluorine, silicon, iron, and manganese, with perhaps a trace of two or three others. The compound elements are of three classes: first, substances of an organic nature introduced with the food, or formed in the processes of digestion and nutrition; secondly, substances resulting from the waste or disintegration of the body; and thirdly, substances of inorganic or mineral origin. The inorganic compound substances are water, chloride of sodium, chloride of potassium, fluoride of calcium, hydrochlorate of ammonia, carbonate of lime, bicarbonate of lime, carbonate of magnesia, carbonate of potassa, bicarbonate of potassa, carbonate of soda, bicarbonate of soda, sulphate of potassa, sulphate of soda, sulphate of lime, basic phosphate of lime or bone earth, acid phosphate of lime, phosphate of magnesia, phosphate of potassa, neutral phosphate of soda, acid phosphate of soda, ammonia, and phosphate of magnesia and ammonia. The compound substances resulting from waste of the human body are principally carbonic acid, urea, creatine, creatinine, urate of soda, and urate of potassa.

The substances of an organic nature related to the nutrition of the body are the uncrystallizable albuminoid matters, such as albumen, albuminose, fibrine, pancreatine, mucosine, musculine, globuline, hema-tine, biliverdine, and melanine; crystallizable substances, either containing nitrogen, such as glycocholate and taurocholate of soda, or destitute of nitrogen, such as sugar and fat. By microscopic observation, the elementary structure of the tissues is found to consist mostly of minute cells, fibres, tubes, and a homogeneous or granular substratum. Schwann believed that all the tissues of the body were formed from cells; but subsequent observation shows that although many tissues retain their original cellular structure throughout life, and many more are formed from cells which are afterward metamorphosed, there are some in which no other cell agency is employed than that which occurs in the elaboration of the plastic material; a certain structureless lamella, commonly called basement membrane, offers no visible traces of cell structure, but rather resembles the filmy tissue of which the walls of minute cells themselves are formed.

It is, however, generally believed that minute cells, or other analogous or derived forms, constitute the elementary organic parts of nearly every tissue, and that all chemical changes occur in them, as integral elements of structure, without altering their numbers and relative positions; that these minute anatomical elements, in fact, are as permanent in form as the tissues and the organs they compose; and that all growth in the individual organism takes place by a relative enlargement of their size, and not by any increase of their number; so that, as the organs remain the same in form and number in the adult as in the new-born child, the same is true of the tissues that compose the organs, and the microscopic cells composing tissues. The principal varieties of cells now recognized are: the red globules of the blood, flattened, circular bodies, homogeneous in structure, from 1/4000 to 1/3000 of an inch in diameter; the white globules of the blood, which are colorless and granular, spherical in form, and 1/2500 of an inch in diameter; scalelike epithelial and epidermic cells, very thin, pentagonal or hexagonal in shape, with a round or oval nucleus imbedded in their substance; columnar and ciliated epithelium cells, lining certain parts of the alimentary canal, air passages, generative organs, and ventricles of the brain; glandular epithelium cells, forming the active agents of secretion in the glandular organs; and the nerve cells of the brain, spinal cord, and ganglia.

The fibres are: the white fibres of areolar tissue, of tendons, fascia?, and the like; the yellow elastic fibres of elastic tissue; the compound muscular fibres; and ultimate nervous filaments. The tubular elements are the capillary blood vessels and lymphatics, and the straight or convoluted tubules of the kidneys, the testicles, and some of the glandular organs. The homogeneous or granular substratum, in which these anatomical elements are imbedded, varies in consistency and composition in the different tissues.