Hygienic Physiology | Page 5

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 lacun?, 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 ends of the bone, thus giving greater size to form a strong joint, while the solid portion increases near the middle, where strength alone is needed. Each fiber of this bulky material diminishes the shock of a sudden blow, and also acts as a beam to brace the exterior wall. The recumbent position of the alligator protects him from falls, and therefore his bones contain very little spongy substance.
In the body, bones are not the dry, dead, blanched things they commonly seem to be, but are moist, living, pinkish structures, covered with a tough membrane, called the per-i-os'-te-um [Footnote: The relations of the periosteum to the bone are very interesting.