Hygienic Physiology : with Special Reference to the Use of Alcoholic Drinks and Narcotics

by Joel Dorman Steele

SAADI.

SELECTED READINGS.

The figures indicate the pages in the text upon which the corresponding subjects will be found.

THE SKELETON.

MAN, AS COMPARED WITH OTHER VERTEBRATE ANIMALS (p. 3).—Man, the lord of the animal kingdom, is constructed after the same type as the cat that purrs at his feet, the ox that he eats, the horse that bears his burden, the bird that sings in his cage, the snake that crawls across his pathway, the toad that hides in his garden, and the fish that swims in his aquarium. All these are but modifications of one creative thought, showing how the Almighty Worker delights in repeating the same chord, with infinite variations. There are marked physical peculiarities, however, which distinguish man from the other mammals. Thus, the position of the spinal opening in the middle third of the base of the skull, thereby balancing the head and admitting an upright posture; the sigmoid S-curve of the vertebral column; the ability of opposing the well-developed thumb to the fingers; the shortened foot, the sole resting flat on the ground; the size and position of the great toe; the length of the arms, reaching halfway from the hip to the knees; the relatively great development of the brain; the freedom of the anterior extremities from use in locomotion, and the consequent erect and biped position. In addition, man is the only mammal that truly walks; that is endowed with the power of speech; and that is cosmopolitan, readily adapting himself to extremes of heat and cold, and making his home in all parts of the globe.—STEELE'S Popular Zoology.

FIG. 68.

[Illustration: Skeleton of Orang, Chimpanzee, and Man.]

UNION OF FRACTURES (p. 8).—In the course of a week after a fracture, there is a soft yet firm substance, something between ligament and cartilage in consistence, which surrounds the broken extremities of the bone, and adheres to it above and below. The neighboring muscles and tendons are closely attached to its surface, and the fractured extremities of the bone lie, as it were, loose in a cavity in the center, with a small quantity of vascular albumen, resembling a semitransparent jelly.

Here, then, is a kind of splint which nature contrives, and which is nearly completed within a week from the date of the accident. We call this new formation the callus. This process goes on, the surrounding substance becoming thicker and of still firmer consistence. In the course of a few days more, the thin jelly which lay in contact with the broken ends of the bone has disappeared, and its place is supplied by a callus continuous with that which formed the original capsule. This is the termination of the first stage of curative progress. The broken ends of the bones are now completely imbedded in a mass of vascular organized substance or callus, something between gristle and cartilage in consistence; and as yet there are no traces of bony matter in it. At this time, if you remove the adventitious substance, you will find the broken ends of bone retaining exactly their original figure and presenting the same appearance as immediately after the fracture took place.

At the end of about three weeks, if you make a section of the callus, minute specks of earthy matter are visible, deposited in it here and there, and at the same time some of the callus, appears to disappear on the outside, so that the neighboring muscles and tendons no longer adhere to it. The specks of bone become larger and more numerous until they extend into each other; and thus by degrees the whole of the callus is converted into bone. Even at this period, however, there is not absolute bony union, for although the whole of the callus has become bone, it is not yet identified with the old bone, and you might still pick it off with a penknife, leaving the broken extremities not materially altered from what they were immediately after the injury. This may be regarded as the end of the second stage of the process by which a fracture is repaired. Now a third series of changes begins to take place. The broken extremities of the bones become intimately united by bony matter passing from one to the other. The mass of new bone on the outside, formed by the ossification of the callus, being no longer wanted, is absorbed; by degrees the whole of it disappears, and the bone is left having the same dimensions which it had before the occurrence of the accident.