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

by Joel Dorman Steele

FIG. 26.

[Illustration: Vertical section of a Molar Tooth, moderately magnified. a, enamel of the crown, the lines of which indicate the arrangement of its columns; b, dentine; c, cement; d, pulp cavity.]

At the center of the tooth is a cavity filled with a soft, reddish-white, pulpy substance full of blood vessels and nerves. This pulp is very sensitive, and toothache is caused by its irritation.

THE FITTING OF THE TOOTH INTO THE JAW is a most admirable contrivance. It is not set like a nail in wood, having the fang in contact with the bone; but the socket is lined with a membrane which forms a soft cushion. While this is in a healthy state, it deadens the force of any shock, but, when inflamed, it becomes the seat of excruciating pain.

THE DECAY OF THE TEETH [Footnote: Unlike the other portions of the body, there is no provision made for any change in the permanent teeth. That part, however, which is thus during life most liable to change, after death resists it the longest. In deep-sea dredgings teeth are found when all traces of the frame to which they belonged have disappeared. Yet hard and incorruptible as they seem, their permanence is only relative. Exposed to injury and disease, they break or decay. Even if they escape accident, they yet wear at the crown, are absorbed at the fang, and, in time, drop out, thus affording another of the many signs of the limitations Providence has fixed to the endurance of our bodies and the length of our lives.] is commonly caused (1) by portions of the food which become entangled between them, and, on account of the heat and moisture, quickly decompose; and (2) by the saliva, as it evaporates, leaving on the teeth a sediment, which we call tartar. This collects organic matter that rapidly changes, and also affords a soil in which a sort of fungus speedily springs up. From both these causes, the breath becomes offensive, and the teeth are injured.

PRESERVATION OF THE TEETH.—Children should early be taught to brush their teeth at least every morning with tepid water, and twice a week with white castile soap and powdered orris root, or with some dentifrice recommended by a responsible dentist. They should also be instructed to remove the particles of food from between the teeth, after each meal, by means of a quill or wooden toothpick.

The enamel once injured is never restored, and the whole interior of the tooth is exposed to decay. We should not, therefore, crack hard nuts, bite thread, or use metal toothpicks, gritty tooth powders, or any acid which "sets the teeth on edge," i. e.. that acts upon the enamel. It is well also to have the teeth examined yearly by a dentist, that any small orifice may be filled, and further decay prevented.

V. THE GLANDS OF THE SKIN.

1. THE OIL GLANDS are clusters of tiny sacs which secrete an oil that flows along the duct to the root of the hair, and thence oozes out on the cuticle (Fig. 24). [Footnote: This secretion is said to vary in different persons, and on that account the dog is enabled to trace his master by the scent.] This is nature's efficient hair-dressing, and also keeps the skin soft and flexible. These glands are not usually found where there is no hair, as on the palm of the hand, and hence at those points only can water readily soak through the skin into the body. They are of considerable size on the face, especially about the nose. When obstructed, their contents become hard and dark-colored, and are vulgarly called "worms." [Footnote: Though they are not alive, yet, under the microscope, they are sometimes found to contain a curious parasite, called the pimple mite, which is supposed to consume the superabundant secretion.]

II. THE PERSPIRATORY GLANDS are fine tubes about 1/300 of an inch in diameter, and a quarter of an inch in length, which run through the cutis, and then coil up in little balls (Fig. 24). They are found in all parts of the body, and in almost incredible numbers. In the palm of the hand, there are about two thousand eight hundred in a single square inch. On the back of the neck and trunk, where they are fewest, there are yet four hundred to the square inch. The total number on the body of an adult is estimated at about two and a half million. If they were laid end to end, they would extend nearly ten miles. [Footnote: The current statement, that they would extend twenty-eight miles, is undoubtedly an exaggeration. Krause estimates the total number at 2,381,248, and the length of each coil, when unraveled, at 1/10 of an inch, which would make the total length much less than even the statement in the text. Seguin states that the proportion of impurities thrown off by the skin and the lungs, is eleven to seven.] The mouths of these glands—"pores," as we commonly call them—may be seen with a pocket lens along the fine ridges which cover the palm of the hand.