When we examine the body from its exterior, we observe that a number of different materials enter into its formation. Hairs, nails, skin, and teeth arc quite different substances ; by feeling through the skin we find harder and softer solid.

What is human anatomy ? Give illustrations of the complexity of the body in structure? Is its internal structure as varied as its external?

State in a few words the subject matters of the sciences of Human Anatomy, Physiology, and Hygiene.

Give examples of the variety of substances entering into the composition of the body. What may we feel through the skin masses under it; while the blood which flows from a cut finger, and the saliva which moistens the mouth, show clearly that liquids exist in the body.

If we were to go farther and examine closely, outside and inside, any one part of the body, the hand for instance, we should find it made up of quite a number of different materials. On its exterior we see skin and nails ; if the skin were dissected off we should find under it more or less yellowish-white fat; beneath the fat would lie a number of red soft masses, the muscles (answering to what we call the lean of meat); under the muscles, again, would be hard, rigid, whitish bones; at the finger joints, where the ends of different bones lie close together, we should find them covered by still another substance, gristle or cartilage. Finally, binding skin and fat and muscles and bone together, we should discover a tough stringy material, quite different from all of them, and which, since it unites all the rest, is called connective tissue. If we took any other portion of the body we should arrive at a similar result; it, too, would be made up of a number of different materials, which materials might, as in the case of the foot, be identical with those found in the hand but arranged together in a different way so as to perform another function (just as wood and nails may be used to build a house or a bridge, but are put together in a different manner in the two cases); or we might, as in the eye, find in addition to some materials found in the hand others quite unlike any of them.

What different materials do we see on looking at a hand ? What others would be found on dissecting away the skin ? What is the technical name for the lean of meat ? What is the technical name of gristle ? What is connective tissue ? Are other parts of the body besides the hand made up of different substances ? Illustrate by an example ?

The branch of anatomy which deals with the characters of the materials used in the construction of the parts of the body is called histology, or, since it is mainly carried on with the aid of the microscope, microscopic anatomy.

Tissues

Each of the different primary building materials which can be distinguished, either with or without the microscope, as entering into the construction of the body, is called a tissue ; we speak, for example, of muscular tissue, fatty tissue, bony tissue, cartilaginous tissue, and so forth ; each tissue has certain properties in which it differs from all the rest, and which it preserves in whatever part of the body it may be found. It also is characterized by certain appearances when examined with a microscope, which are the same for the same tissue no matter where it is found. The total number of important tissues is not great; the variety in structure and use which wo find in the parts of the body depends mainly on the diverse ways in which the same tissues are combined together, over and over again, in different parts.

Organs

A portion of the body composed of several tissues, and specially fitted for the performance of a particular duty or function, is called an organ ; thus, the hand is an organ of prehension ; the eye, the organ of sight; the stomach, an organ of digestion; and so forth.

Summary

The human body is made up of a limited number of tissues ;* each tissue has a characteristic ap.

What is histology? Give another name for it.

What is a tissue? Give examples. How do tissues differ? Are there a large number of important tissues ? How is the variety in structure of the parts of the body produced?

What is an organ? Give examples. Of what is the body made up ?

* The various tissues of the body will be considered in more detail subsequently: the more important areó1. Bony tissue. 2. Cartilaginous tissue. 3. White fibrous pearance, by which it can be recognized with the microscope, and some one or more distinctive properties which fit it for some special use ; thus, it may be very tough, and suited for binding other parts together; or rigid, and adapted to preserve the shape of the body ; or have the power of changing its length and be useful for moving parts to which its ends are attached.

The tissues are variously combined to form the organs of the body, of which there are very many, differing in size, shape, and structure ; some organs contain only a few tissues ; others, a great many; some possess only tissues which are found also in other organs, others contain on0 or more tissues peculiar to themselves ; but wherever an organ is found, it is constructed and placed with reference to the performance of some duty ; the organs are the machines which are found in the factory represented by the body, and the tissues are the materials used in building the machines ; or, using another illustration, we may, with Longfellow, compare the body to a dwelling-house ; and then go on to liken the tissues to the brick, stone, mortar; wood, iron, and glass, used in building it; and the organs to the walls, floors, ceilings, doors, and windows, which, made by combining the primary building materials in different ways, have each a purpose of their own, and all together make the house.

How are tissues recognized ? Give examples of differences in properties of various tissues.

How do organs differ from one another ? In what do all organs agree ? Illustrate the relation of organs and tissues to the body: as a whole ? connective tissue. 4. Yellow elastic tissue. 5. Glandular tissue, of which there are many varieties. 6. Respiratory tissues. 7. Fatty tissue. 8. Sense-organ or irritable tissues. 0. Nerve cell tissue. 10. Nerve fiber tissue. 11. Striped muscular tissue. 12. Unstriped muscular tissue. 18. Epidermic and epithelial tissue.