Part 14 (1/2)

How is this shown by experiment? 207. Upon what do the different intonations of sound or mechanical employments depend? Why are the first efforts in educating the muscles indifferent or irregular? 208.

Why is repet.i.tion of muscular action necessary? Why is it important that correct movements be adopted in the first efforts of muscular education?

_Ill.u.s.tration._ If a boy, while learning to mow, is allowed to swing his scythe in a stooping position, twisting his body at every sweep of the scythe, he will never become an easy, efficient mower. Proper instruction is as necessary in many of the agricultural branches as in the varied mechanical employments.

[Ill.u.s.tration: Fig. 52. An improper, but not an unusual position, when writing.]

[Ill.u.s.tration: Fig. 53. A proper position, when writing.]

209. _Good penmans.h.i.+p requires properly trained muscles._ To a deficient a.n.a.lysis of the movements of the arm, hand, and fingers, on the part of teachers and pupils in penmans.h.i.+p, together with an improper position in sitting, is to be ascribed the great want of success in acquiring this art. The pen should be held loosely, and when the proper position is attained, the scholar should make an effort to imitate some definite copy as nearly as possible. The movements of the fingers, hand, and arm, necessary to accomplish this, should be made with ease and rapidity, striving, at each effort, to imitate the copy more nearly.

How is this ill.u.s.trated? 209. Why have so many pupils failed in acquiring good penmans.h.i.+p?

210. When the arm, hand, and fingers are rigid, the large muscles, that bend and extend these parts, are called into too intense action.

This requires of the small muscles, that produce the lateral movements, which are essential to rapidity in writing, an effort which they cannot make, or can with difficulty accomplish.

_Experiment._ Vigorously extend the fingers by a violent and rigid contraction of the muscles upon the lower part of the arm, and the lateral movement which is seen in their separation cannot be made. But gently extend the fingers, and their oblique movements are made with freedom.

211. An individual who is acquainted with the laws of health, whose muscles are well trained, will perform a certain amount of labor with less fatigue and waste to the system, than one who is ignorant of the principles of hygiene, and whose muscles are imperfectly trained.

Hence the laboring poor have a deep interest in acquiring a knowledge of practical physiology, as well as skill in their trade or vocation.

It is emphatically true to those who earn their bread by the ”sweat of their brow,” that ”knowledge is power.”

210. What is said of the lateral and oblique movements of the arm, hand, and fingers in writing? How is this shown by experiment? 211.

Why is the study of physiology and hygiene of utility to the laborer?

CHAPTER XII.

THE TEETH.

212. The teeth, in composition, nutrition, and growth, are different from other bones of the body. They vary in number at different periods of life, and, unlike other bones, they are exposed to the immediate action of atmospheric air and foreign substances. The bones of the system, generally, when fractured, unite; but there is never a permanent union of a tooth when broken.

ANATOMY OF THE TEETH.

213. The TEETH are attached to the upper and lower jaw-bone, by means of bony sockets, called _alve-o-lar_ processes. These give great solidity to the attachment of the teeth, and frequently render their extraction difficult. The gums, by their fibrous, fleshy structure, serve to fix the teeth more firmly in the jaw.

_Observation._ When a _permanent_ tooth is extracted, these bony processes are gradually absorbed, so that in advanced age there remains only the jaw-bone covered by the lining membrane of the gum.