Experiment 1. To examine squamous epithelium. With an ivory paper-knife scrape the back of the tongue or the inside of the lips or cheek; place the substance thus obtained upon a glass slide; cover it with a thin cover-glass, and if necessary add a drop of water.  Examine with the microscope, and the irregularly formed epithelial cells will be seen.

Experiment 2. To examine ciliated epithelium. Open a frog’s mouth, and with the back of a knife blade gently scrape a little of the membrane from the roof of the mouth.  Transfer to a glass slide, add a drop of salt solution, and place over it a cover-glass with a hair underneath to prevent pressure upon the cells.  Examine with a microscope under a high power.  The cilia move very rapidly when quite fresh, and are therefore not easily seen.

For additional experiments which pertain to the microscopic examination of the elementary tissues and to other points in practical histology, see Chapter XV.

[NOTE.  Inasmuch as most of the experimental work of this chapter depends upon the use of the microscope and also necessarily assumes a knowledge of facts which are discussed later, it would be well to postpone experiments in histology until they can be more satisfactorily handled in connection with kindred topics as they are met with in the succeeding chapters.]

Chapter II.

The Bones.

27.  The Skeleton.  Most animals have some kind of framework to support and protect the soft and fleshy parts of their bodies.  This framework consists chiefly of a large number of bones, and is called the skeleton.  It is like the keel and ribs of a vessel or the frame of a house, the foundation upon which the bodies are securely built.

There are in the adult human body 200 distinct bones, of many sizes and shapes.  This number does not, however, include several small bones found in the tendons of muscles and in the ear.  The teeth are not usually reckoned as separate bones, being a part of the structure of the skin.

The number of distinct bones varies at different periods of life.  It is greater in childhood than in adults, for many bones which are then separate, to allow growth, afterwards become gradually united.  In early adult life, for instance, the skull contains 22 naturally separate bones, but in infancy the number is much greater, and in old age far less.

The bones of the body thus arranged give firmness, strength, and protection to the soft tissues and vital organs, and also form levers for the muscles to act upon.

28.  Chemical Composition of Bone.  The bones, thus forming the framework of the body, are hard, tough, and elastic.  They are twice as strong as oak; one cubic inch of compact bone will support a weight of 5000 pounds.  Bone is composed of earthy or mineral matter (chiefly in the form of lime salts), and of animal matter (principally gelatine), in the proportion of two-thirds of the former to one-third of the latter.