arrangement of compact and cancellous tissue.)]

Experiment 5. Obtain a part of a beef shin bone, or a portion of a
sheep's or calf's leg, including if convenient the knee joint. Have the
bone sawed in two, lengthwise, keeping the marrow in place. Boil,
scrape, and carefully clean one half. Note the compact and spongy parts,
shaft, etc.

Experiment 6. Trim off the flesh from the second half. Note the
pinkish white appearance of the bone, the marrow, and the tiny specks of
blood, etc. Knead a small piece of the marrow in the palm; note the oily
appearance. Convert some marrow into a liquid by heating. Contrast this
fresh bone with an old dry one, as found in the fields. Fresh bones
should be kept in a cool place, carefully wrapped in a damp cloth, while
waiting for class use.

A fresh or living bone is covered with a delicate, tough, fibrous
membrane, called the periosteum. It adheres very closely to the bone,
and covers every part except at the joints and where it is protected with
cartilage. The periosteum is richly supplied with blood-vessels, and plays
a chief part in the growth, formation, and repair of bone. If a portion of
the periosteum be detached by injury or disease, there is risk that a
layer of the subjacent bone will lose its vitality and be cast off.[5]

30. Microscopic Structure of Bone. If a very thin slice of bone be
cut from the compact tissue and examined under a microscope, numerous
minute openings are seen. Around these are arranged rings of bone, with
little black bodies in them, from which radiate fine, dark lines. These
openings are sections of canals called _Haversian canals_, after Havers,
an English physician, who first discovered them. The black bodies are