Hygienic Physiology | Page 5

solid oak.] and also a larger surface for the
attachment of the muscles.
The Composition of the Bones at maturity is about one part animal to
two parts mineral matter. The proportion varies with the age. In youth it
is nearly half and half, while in old age the mineral is greatly in excess.
By soaking a bone in weak muriatic acid, and thus dissolving the
mineral matter, its shape will not change, but its stiffness will disappear,
leaving a tough, gristly substance [Footnote: Mix a wineglass of
muriatic acid with a pint of water, and place in it a sheep's rib. In a day
or two, the bone will become so soft that it can be tied into a knot. In
the same way, an egg may be made so pliable that it can be crowded
into a narrow- necked bottle, within which it will expand, and become
an object of great curiosity to the uninitiated. By boiling bones at a high
temperature, the animal matter separates in the form of gelatine. Dogs
and cats extract the animal matter from the bones they eat. Fossil bones
deposited in the ground during the Geologic period, were found by
Cuvier to contain considerable animal matter. Gelatine was actually
extracted from the Cambridge mastodon, and made into glue. A
tolerably nutritious food might thus be manufactured from bones older
than man himself.] (cartilage) which can be bent like rubber.
If the bone be burned in the fire, thus consuming the animal matter, the
shape will still be the same, but it will have lost its tenacity, and the
beautiful, pure-white residue [Footnote: From bones thus calcined, the
phosphorus of the chemist is made. See Steele's "Popular Chemistry,"
page 114. If the animal matter be not consumed, but only charred, the
bone will be black and brittle. In this way, the "boneblack" of
commerce is manufactured.] may be crumbled into powder with the
fingers.
FIG. 2.
[Illustration: The Thigh Bone, or Femur, sawed lengthwise.]
We thus see that a bone receives hardness and rigidity from its mineral,
and tenacity and elasticity from its animal matter.

The entire bone is at first composed of cartilage, which gradually
ossifies or turns to bone. [Footnote: The ossification of the bones on the
sides and upper part of the skull, for example, begins by a rounded spot
in the middle of each one. From this spot the ossification extends
outward in every direction, thus gradually approaching the edges of the
bone. When two adjacent bones meet, there will be a line where their
edges are in contact with each other, but have not yet united; but when
more than two bones meet in this way, there will be an empty space
between them at their point of junction. Thus, if you lay down three
coins upon the table with their edges touching one another, there will
be a three-sided space in the middle between them; if you lay down
four coins in the same manner, the space between them will be
four-sided. Now at the back part of the head there is a spot where three
bones come together in this way, leaving a small, three-sided opening
between them: this is called the "posterior fontanelle." On the top of the
head, four bones come together, leaving between them a large,
four-sided opening: this is called the "anterior fontanelle." These
openings are termed the fontanelles, because we can feel the pulsations
of the brain through them, like the bubbling of water in a fountain.
They gradually diminish in size, owing to the growth of the bony parts
around them, and are completely closed at the age of four years after
birth.--DALTON.] Certain portions near the joints are long delayed in
this process, and by their elasticity assist in breaking the shock of a fall.
[Footnote: Frogs and toads, which move by jumping, and consequently
receive so many jars, retain these unossified portions (epiphyses) nearly
through, life, while alligators and turtles whose position is sprawling,
and whose motions are measured do not have them at all--LEIDY]
Hence the bones of children are tough, are not readily fractured, and
when broken easily heal again; [Footnote: This is only one of the many
illustrations of the Infinite care that watches over helpless infancy, until
knowledge and ability are acquired to meet the perils of life.] while
those of elderly people are liable to fracture, and do not quickly unite.
FIG. 3.
[Illustration: _A thin slice of Bone, highly magnified showing the
lacunæ, the tiny tubes (canaliculi) radiating from them, and four

Haversian canals, three seen crosswise and one lengthwise._]
THE STRUCTURE OF THE BONES--When a bone is sawed
lengthwise, it is found to be a compact shell filled with a spongy
substance This filling increases in quantity, and becomes more porous
at the