462 ANATOMY purified and renovated in the lungs, the blood returns to the left side of the heart, performing a complete circuit in the region of the heart and lungs alone, for this sole purpose. It is then propelled from the left ventricle of the heart, through the aorta and all the arteries of the whole body, into every organ, for the pur- pose of nutrition. The capillary vessels ramify minutely in every organ, and the tissues of the part absorb the nutrient portions of the fluid, and return waste matter to the veins, in ex- change for the nutriment brought to them by the arteries. The general system of arteries carries pure blood to all parts of the body, and the general system of veins returns' impure blood from all parts of the body back into the heart, to be thence sent into the lungs for puri- fication, and thus keep up perpetual circulation and renovation. 3d. The respiratory organs are the larynx, the trachea or windpipe, the bronchial tubes, and air vesicles within the lungs. Their function is to breathe in new sup- plies of air to vivify the blood, and to exhale carbonic acid and other vitiated matters, which are poisonous when accumulated in too large a quantity. 4th. The kidneys separate from the blood the elements of the urine, and thus rid the system of another kind <of waste matter, which also becomes poisonous if allowed to accumulate within the vessels that contain and circulate the vital fluid. When in the bladder the urine is not dangerous, because no longer mingled with the blood, unless too much accu- mulated and too long retained. To the third class of organs belong the reproductive systems, male and female. These are not essential to the life of the individual, as they may be ex- tirpated without danger even to the health. General anatomy treats of the different sorts of tissue composing the organs of the body. 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, &c. Serous mem- brane 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 peri- toneum as a covering for the viscera of the abdomen, and a lining for the inner walls of the trunk be^ow the chest. The leading ele- ments of structure in the organs of the body are fibrous tissue, serous membrane, bony texture, cartilaginous texture, fibro-cartilage, muscular fibre ofXyarious kinds, striated and non-striated, glandular tissue, mucous mem- brane, 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 sub- stance, and gray nervous or ganglionic or vesicular matter; and diseases -are character- ized 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, nitro- gen, 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 or- ganic nature introduced with the food, or formed in the processes of digestion and nutrition ; sec- ondly, substances resulting from the waste or disintegration of the body; and thirdly, sub- stances of inorganic or mineral origin. The in- organic compound substances are water, chlo- ride of sodium, chloride of potassium, fluoride of calcium, hydrochlorate of ammonia, carbon- ate 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, sul- phate of lime, basic phosphate of lime or bone earth, acid phosphate of lime, phosphate of mag- nesia, 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 mat- ters, such as albumen, albuminose, fibrine, pan- creatine, mucosine, musculine, globuline, hema- tine, biliverdine, and melanine ; crystallizable substances, either containing nitrogen, such as glycocholate and taurocholate of soda, or des- titute of nitrogen, such as sugar and fat. By microscopic observation, the elementary struc- ture 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 after- ward 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, com- monly called basement membrane, offers no visible traces of cell structure, but rather re- sembles the filmy tissue of which the walls of minute cells themselves are formed. It is, how- ever, generally believed that minute cells, or other analogous or derived forms, constitute
