Chapter XV

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83 On account of the striations of these cells the muscles which they form are called striated muscles.

84 The striated muscle cells, having many nuclei, are said to be multi-nucleated.

85 Every movement in the body has its opposing movement. This is necessary both on account of the work to be accomplished and for preserving the natural form of the body.

86 The distance from the fulcrum to the power is called the _power-arm_ and the distance from the fulcrum to the weight is called the _weight-arm_ (Fig. 115).

87 The foot in lifting the body on tiptoe appears at first thought to be a lever of the second class, the body being the weight and the toe serving as the fulcrum. However, if the distance which the body is raised is compared with the distance which the muscle shortens, it is found that the _supposed_ weight has moved _farther_ than the power (Fig. 118). It will also be noted that the muscle which furnishes the power is attached at its upper end to the "weight." These facts show clearly that we are not here dealing with a lever of the second class. The foot in this instance acts as a lever of the first class with the fulcrum at the ankle joint and the toe pressing against the earth, which is the _actual_ weight. Since the earth is immovable, the body is lifted or pushed upward, somewhat as a fulcrum support is made to move when it is too weak to hold up the weight that is being lifted. In other words, we have the same lever

## action in the foot in lifting the body as we have when one lies face

downward, and, bending the knee, lifts some object on the toes.

_ 88 Walking_ is considered one of the very best forms of counter-active exercise for the brain worker (page 328).

89 The epidermis does not afford complete protection against chemicals, many of them being able to destroy it quickly. The rule of washing the skin immediately after contact with strong chemical agents should always be followed.

90 "Rough calculations have placed the number of sweat glands on the entire body at about 2,000,000." Rettger, _Studies in Advanced Physiology_.

91 Heat also leaves the body by the lungs, partly by the respired air and partly through the evaporation of moisture from the lung surfaces. Respiration in some animals, as the dog, is the chief means of cooling the body.

92 "The story is told of some woodsmen who were overtaken by a severe snowstorm and had to spend the night away from camp; they had a bottle of whisky, and, chilled to the bone, some imbibed freely while others refused to drink. Those who drank soon felt comfortable and went to sleep in their improvised shelter; those who did not drink felt very uncomfortable throughout the night and could get no sleep, but in the morning they were alive and able to struggle back to camp, while their companions who had used alcohol were frozen to death.... This, if true, was of course an extreme case; but it accords with the universal experience of arctic travelers and of lumbermen and hunters in the northern woods, that the use of alcohol during exposure to cold, although contributing greatly to one's comfort for the time being, is generally followed by undesirable or dangerous results."--HOUGH AND SEDGWICK: _The Elements of Hygiene and Sanitation_.

93 Foods that are difficult to digest, or which cause disturbances of the digestive organs (a coated tongue being one indication), have a bad effect upon the skin. It is in this way that the use of tea and coffee by some people induces a sallow or "muddy" condition of the complexion.

94 A most valuable antiseptic ointment is prepared by the druggist from the following formula:

Lanolin, 25 grams. Ichthyol, 6 grams. Yellow vaseline, 20 grams.

This is applied as a thin layer on the surface, except in the case of boils or abscesses. In treating these a heavy layer is spread over the affected part and then covered with absorbent cotton or a thin piece of clean cotton cloth.

95 In a larger sense adjustment includes all those activities by means of which the body is brought into proper relations with its environment, including the changes which the body makes in its surroundings to _adapt them_ to its purposes.

96 Almost to the present time, physiologists have described the nervous system as being made up of two kinds of structural elements which were called _nerve cells_ and _nerve fibers_. The nerve cells were supposed to form the ganglia and the fibers to form the nerves. Recent investigators, however, employing new methods of microscopic study, have established the fact that the so-called nerve cell and nerve fiber are but two divisions of the same thing and that the nervous system is made up of, not two, but one kind of structural element. The term "neuron" is used to denote this structural element, or _complete nerve cell_.

97 Many of the axons in the brain and spinal cord have no primitive sheath. Axons without the medullary sheath are found in the sympathetic nerves. These are known as non-medullated axons and they have a gray instead of a white color.

98 The difference in weight between the brain of man and that of woman is due mainly to the fact that man's body is, as a rule, considerably larger than that of woman's.

99 The nervous tissues present, at different places, two colors--one white, and the other a light gray. Great significance was formerly attached to these colors, because it was supposed that they represented two essentially different kinds of nervous matter. It is now known that the protoplasm in all parts of the neuron proper--cell-body, axis cylinder, and dendrites--has a grayish color, while the coverings of most of the fibers are white. Hence gray matter in any part of the nervous system indicates the presence of cell-bodies, and white matter the presence of nerve fibers.

100 In very early life the spinal cord entirely fills the spinal cavity, but as the body develops the cord grows less rapidly than the spinal column, and, as a consequence, separates at the lower end from the inclosing bony column.

101 Fibers passing between the spinal cord and the cerebrum cross to opposite sides--most of them at the bulb, but many within the cord--so that the right side of the cerebrum is connected with the left side of the body, and _vice versa_. This accounts for the observed fact that disease or accidental injury of one side of the cerebrum causes loss of motion or of feeling in the opposite side of the body.

102 In general, _afferent_ neurons or fibers are those that convey impulses _toward_ the central nervous system (brain and cord), while _efferent_ neurons or fibers are those that convey impulses _from_ the central system.

103 At different times the nervous impulse has been regarded as a current of electricity; as a progressive chemical change, likened to that in a burning fuse; as a mechanical vibration, such as may be passed over a stretched rope; and as a molecular disturbance accompanied by an electrical discharge. The velocity of the nervous impulse, which is only about one hundred feet per second, proves that it is not a current of electricity. It takes place with little or no exhaustion of the cell protoplasm and consequently is not due to chemical action. And the loose, relaxed condition of the nerves prevents their transmission of physical vibrations, like those on a stretched rope. The view that the impulse is a progressive molecular disturbance, accompanied by an electrical discharge, has much evidence in its favor, but it has only recently been proposed and is likely to be modified upon fuller investigation.

104 The surface of the body includes the linings of the air passages, food canal, and certain cavities, as well as the external covering or skin.

105 Derived from the Latin _re_, back, and _flectere_, to turn or bend.

106 A frog from which the brain has been removed is suspended with its feet downward and free to move. If a toe is pinched, the foot is drawn away, and if dilute acid, or a strong solution of salt, is placed on the tender skin, the feet are moved as if to take away the irritating substance. This of course shows that reflex action can take place independently of the brain.

Now if the spinal cord is also destroyed, there is no response when the irritation of the skin is repeated. The animal remains perfectly quiet, because the destruction of the cord has interrupted the reflex action pathway. This shows that some part of the central nervous system is necessary to reflex action.

107 Review description of the spinal nerves, page 295.

108 Where a deep-seated cause for worry exists, there may be occasion for grave concern. Many people have become insane through continued worry about some _one_ thing. In cases of this kind the sufferer needs the aid of sympathetic friends, and sometimes of the physician, in getting the mind away from the exciting cause. A change of scene, a visit, or some new employment is frequently recommended, where the actual cause for the worry cannot be removed.

109 Any part of the body which is overworked or which works at a disadvantage tends to disturb, more or less, the entire nervous system and to produce nervousness. Especially is this true of such delicate and highly sensitive structures as the eyes. If the eyes do not focus properly or if the muscles that move the eyeballs are out of their natural adjustment, extra work is thrown upon these delicate parts. One of the first and sometimes the only indication of eye strain is that of some disturbance of the nervous system. For this reason it is important to carefully test the eyes in determining the cause of nervousness (page 385).

110 One form of neck exercise recommended for this purpose is easily taken on retiring at night. Lying flat on the back, without a pillow, lift the head slowly from the bed and let it as slowly settle back to the level of the body. Repeat several times, lying on the back, and then again on the face and again on each side. Practice these exercises every night during an interval of a month or until relief is secured.

111 Insurance statistics show that habitual _moderate drinkers_ do not live so long as abstainers.

112 Organs very frequently affected by tobacco are the heart and the eyes. It induces, as already stated (page 56), a dangerous nervous derangement called "tobacco heart," and it causes a serious disorder of the retina (retinitis) which leads in some instances to loss of vision. Tobacco smoke also acts as an irritant to the delicate lining of the eyes, especially when the tobacco is smoked indoors.

113 Of 4117 boys in the Illinois State Reformatory, 4000 used tobacco, and over 3000 were cigarette smokers. Dr. Hutchison, of the Kansas State Reformatory, says: "Using cigarettes is the cause of the downfall of more of the inmates of this institution than all other vicious habits combined."

114 The term "mind" is used in this and preceding chapters in its popular, not technical, sense.

115 The problem of social adjustment is but a phase of the general problem of establishing proper relations between the body and its surroundings.

116 A vibrating body is one having a to-and-fro movement, like that of a clock pendulum or the string of a violin on sounding. Bodies to give out sound waves must vibrate rapidly, making not less than sixteen vibrations per second. The upper limit of hearing being about 40,000 vibrations per second, certain bodies may even vibrate too rapidly to be heard.

117 Somewhat as the waves on a body of water impart motion to the sticks and weeds along the shore, sound waves are able to cause bodies that are small or that are delicately poised to vibrate.

118 Some idea of how the movements of the cartilages change the tension of the cords may be obtained by holding the fingers on the larynx, between the thyroid and cricoid cartilages, and making tones first of low and then of high pitch. For the high tones the cartilages are pulled together in front, and for the low tones they separate. As they pull together in front, they of course separate behind and above, where the cords are attached.

119 It is only the central portion of the pinna that aids the entrance of sound into the auditory canal. If by accident the outer portion of the pinna is removed, there is no impairment of the hearing.

120 The middle ear is also called the _ear drum_, and, by the same system of naming, the membrana tympani is referred to as the _drum membrane_.

121 The inner projection of the temporal bone is known as the petrous process.

122 A small opening in the bone at this place is called the _fenestra rotunda_.

123 Consult some work on physics on the different kinds of lenses and their uses.

124 With respect to its adjustments the eye does not differ in principle from various other optical instruments, such as the microscope, telescope, photographer's camera, etc., which, in their use, form images of objects. These all require some adjustment of their parts, called focusing, which adapts them to the distance. The eye's method of focusing, however, differs from that of most optical instruments, in that the adjustment is brought about through changes in the curvature of a lens.

125 The converging power of convex lenses varies as the curvature--the greater the curvature, the greater the converging power.

126 An oculist is a physician who specializes in diseases of the eye.

127 Some of the more common symptoms of eye strain are nervousness, headache, insomnia, irritations of the eyelids, sensitiveness to bright light, and pain in the use of the eyes.

128 Pyle, _Personal Hygiene_.

129 "An infectious disease is one in which disease germs infect (that is, invade) the body from without. Among the infectious diseases are some that are quite directly and quickly conveyed from person to person and to these the term contagious is applied. Formerly a sharp line was drawn between infection and contagion, but to-day it is recognized that no such line exists."--HOUGH AND SEDGWICK, _The Elements of Hygiene and Sanitation._

130 The arctic explorer, Nansen, states that during all the time that his party was exposed to the low temperature of the arctic region, no one was attacked by a cold, but on returning to a warmer climate they were subject to colds as usual. The difference he attributes to the absence of germs in the severe arctic climate. There seems to be no doubt but that most of our common colds are due to attacks of germs.

131 An interesting biological fact is that the female _Anopheles_, and not the male, sucks the blood of animals and is the cause of the spreading of malaria.

132 The habit of spitting upon the floors of public buildings and street cars, and also upon sidewalks, is now recognized as a most dangerous practice. Not only consumptives, but people with throat affections, may do no end of harm in the spreading of disease by carelessness in this respect.

133 For further information on the care of consumptives, consult Huber's _Consumption and Civilization_.

134 As typhoid fever is a disease of the small intestine, great care must be exercised in taking food and in the bodily movements. Solids greatly irritate the diseased lining of the intestine, and the weakened walls may actually be broken through by pressure resulting from moving about.

135 Alcoholic beverages include all the various kinds of drinks that owe their stimulating properties to a substance, ethyl alcohol (C2H5OH), which is made from sugar by the process of fermentation. They include _malt liquors_, such as beer and ale, which contain from three to eight per cent of alcohol; _wines_, such as claret, hock, sherry, and champagne, which contain from five to twenty per cent of alcohol; and _distilled liquors_, such as brandy, whisky, rum, and gin, which contain from thirty to sixty-five per cent of alcohol. Alcoholic beverages all contain constituents other than alcohol, these varying with the materials from which they are made and with the processes of manufacture. The distilled liquors are so called from the fact that their alcohol has been separated from the fermenting substances by distillation.

136 Duncan, _The Chemistry of Commerce_.

137 Alcohol is "denatured" by adding substances to it such as wood alcohol, which render its use as a beverage impossible.

138 The tobacco plant, _Nicotiana tobacum_, is a native of America, and the use of tobacco began with the American Indians. It was taken back to Europe by the early explorers, Sir Walter Raleigh being credited with introducing it to the nobility of England.

139 Most headaches are the result either of eye strain or of digestive disturbances, such as indigestion and constipation, and are to be relieved through the work of the oculist or through attention to the hygiene of the digestive system.