4. The fresh air must be warmed before being introduced into the schoolroom. The temperature of this fresh air as it comes into the room should not, as a rule, exceed 100° F. 5. There is general agreement that in a schoolroom the outlet should be near the floor on the inner wall or corner of the room; that the inlet should be about seven or eight feet above the floor on the same side. 6. The same principles should be followed in heating and ventilating a small schoolhouse of one room as in the case of larger buildings. The stove should be surrounded with an air space enclosed by a jacket of sheet-iron. Fresh air should be introduced into this space through a flue connecting with the outer air. The bad air should be exhausted by an outlet into the chimney, near the floor. 7. As many teachers are obliged to teach in schoolhouses that have no proper means of heating and ventilation, they should learn to make the best of bad conditions. This can be done by the greater regard for cleanliness, and by considering the general laws of air currents. Each room presents each day a new problem in ventilation, to be solved only by considering many factors, the position of the windows in relation to the heating apparatus, the direction of the wind, the humidity of the atmosphere, the difference between the outdoor and indoor temperature, etc. If the conditions are so bad that the room cannot possibly be ventilated properly, then the way to keep the pupils in good health and to make them do the maximum amount of work is to have frequent recesses, during which the room is flooded with fresh air by opening the windows. 8. The greatest cleanliness and the best possible system of heating and ventilation are desirable, for pedagogic as well as for hygienic WM. H. BURNHAM, Clark University. reasons. Worcester, Mass. Introduction, Some Fundamental Truths About the Human Body discussion of the child should ever lose sight of the fact that he is a complicated piece of machinery, possessed of a definite structure, and capable equally of de velopment or of impairment, according as that structure be considered or disregarded. In some ways this chapter should have stood first; yet its position at the close, after the total environment of school life has been discussed and some of the causes of danger and failure pointed out, emphasizes the absolute necessity of considering the structure of the body as a fundamental factor in deciding the precise character of the educational environment in its widest sense. Every teacher should be thoroughly acquainted with the anatomy and physiology of the human body, and with the changes it undergoes during growth; in no other way can the environment of the school be planned so as to avoid dangers which threaten the future health of the adult, and so as to attain a perfect, well-rounded development of mind and body. That excellent system of First Aid to the Injured, propagated by the Red Cross Society, should also be as familiar in our own land as it already is in other countries. It is evidently impossible in the limited space at hand to give a comprehensive view of human anatomy and physiology; but all will have access to texts on the subject, and it was thought that greater emphasis should be laid here on those topics of most immediate hygienic importance in the schoolroom which had not received attention at the hands of others in the preceding pages. Very many will not agree with the list of topics chosen for consideration here, or with the relative prominence assigned to each. Any selection involves difference of opinion, and no defense of that made here will be attempted. It is, however, the sincere hope of the writer that this short and imperfect discussion may stimulate many to a broader study of the subject, and to a more constant and consistent application of their knowledge to the work of the schoolroom. The bony skeleton. about two hundred separate parts or bones, which, though very unlike in shape and relation to each other, are uniform in composition. At first composed of a tough rubber-like substance known as cartilage, they are gradually hardened by changes involving the deposition of mineral substances, chiefly salts of lime, until in the aged they have become extremely brittle. In young children large portions of all bones are still cartilaginous, and in all long bones, such as the femur or humerus, there may be found plates of cartilage separating the well-ossified shaft from the ends of the bone, both of which are also thoroughly indurated by lime. This condition obtains until comparatively late in life, and permits of the growth of the bone through the addition to the calcified portions of successive layers of osseous tissue. Ultimately the three parts are firmly knit together, although this does not occur until about the twenty-first year. The separate bones of the pelvis do not unite until several years later. Thus, throughout the entire period of school life the skeleton is incomplete, and strains of various kinds to which it may be unduly subjected readily produce serious results. Numerous instances of this have already been cited in the chapter on physical defects of children. The gradual formation of bone by the deposition of mineral substances throws light also on the character of food which should be given to young children. In case the nutritive substances are lacking in the mineral salts, there is as a result imperfect bone formation and accompanying weakness. The various bones of the skeleton, which are shown in the accompanying illustration (Fig. 1), fall naturally into four groups: 1. An axial series of parts, the vertebræ, composing the backbone or spinal column, together with the ribs and sternum, which form the framework of the chest or thorax. 2. The bones of the legs, together with the pelvis, the girdle by which they are joined to the axial column. 3. The bones of the arms, with the shoulder girdle, affording a corresponding attachment for these appendages. 4. The bones of the skull. Of the spinal column as a whole it may be The framework of the body is made up of said that the bones are separated by small the front results in the unequal compression of the intervertebral pads, with the effect of modifying the normal curvatures and producing the defect known as "round shoulders" in one case, or causing an unnatural lateral curvature in the other case. The most common causes of these difficulties are probably incorrect attitudes in reading or writing, and school desks or chairs of improper height. The most characteristically human feature about the bones of the leg may be found in the arched instep, by reason of which the jar of walking is broken, since the bones in the arch move slightly over one another and impart a peculiar elasticity to the step. This feature is of great importance in walking, and Martin says: "In London flat-footed policemen are rejected, as they cannot stand the fatigue of walking the daily 'beat.'" The bones of the skull fall naturally into two groups, those of the brain-case or cranium, and those of the face. On examination of the skull in its lateral aspect, an irregular line dividing the two portions may be traced from the upper limit of the nose to the inner angle of the lower jaw. The facial skeleton composes, here, but a small fraction of the entire mass, and is furthermore overtowered by the strongly developed frontal portion of the braincase, which also extends well back beyond the large opening on the lower surface, through which the cavity of the column communicates with that of the skull. If with this is compared the skull of a dog or cat, the relatively smaller size and lesser projection of the facial skeleton in the human skull will be apparent at once, while the superior development of the brain-case is equally striking. The human skull is, moreover, so nearly balanced on the top of the vertebral column that it appears to be in equipoise; in those lower animals, however, which assume at times an upright position, the overbalanced condition of the head due to the projecting face and poorly developed cranium is very apparent, as is also the muscular effort necessary to hold the head upright. thoracic and sacral curvatures the convexity The joints. is directed backwards. The various vertebræ turn slightly upon each other with a sliding motion, so that the entire structure has a power of movement far beyond that of an ordinary rod-like axis. This is compensated for, however, by an increased liability to distortion. Continual leaning toward one side or toward The parts of the skeleton which have been described in brief are not all similarly related to each other. In some places the bones are firmly united by irregular edges, which fit into each other and produce the solid union shown in the skull; such joints are known as sutures and are immovable. Movable joints are grouped, according to the character of the movement, into (a) gliding joints, such as are found between the vertebræ; (b) hinge joints, shown between the phalanges; (c) pivotal joints, best illustrated by the movement of the atlas on the axis; (d) ball and socket joints, of which the shoulder and hip joints are good examples. There is a regular increase in the freedom of motion allowed in the joints, from the extremely limited movement of the gliding joint to the full sweep of the ball and socket joint. In spite of this difference, the structure of all movable joints is fundamentally the same. The contiguous bony surfaces are covered with a thin layer of articular cartilage, which affords a smooth surface. A loose saccular ligament forms a capsule covering the joint, and connecting the bones are also other ligaments, usually in the form of bands. The inside of the capsular ligament and the surfaces of the articular cartilages are covered by a thin membrane, which secretes a lubricating fluid and forms the lining of the joint; in this way friction is reduced to a minimum. In addition to the various ligaments, which are strong and pliable but entirely non-elastic, and hence serve to keep the bones in place, two other factors aid in maintaining the normal arrangements of the parts, namely, the form of the bones themselves, with the cartilage rim of the joint, and the pull of the muscles which pass from the bones on one side of the joint to those on the other. In addition to this, the pressure of the air exerts an influence in retaining the bones in place. Despite these influences, it happens at times that a wrench or sudden strain throws one of the bones out of place. The effect of such a dislocation is seen in the swelling and inflammation which follow soon after the injury; and the continued pull of the muscles attached to the displaced bone tends to aggravate the injury which has been done the ligaments and other parts. The reduction of the dislocation is, hence, a matter of immediate importance, and should not be undertaken by an unskilled person. After the injury long continued rest is necessary to give the broken ligaments time to unite. Medical adMedical advice should always be obtained if the inflammation does not subside at once, since a trivial injury may otherwise result in a permanently stiffened joint. The muscular system. eral by the masses of flesh or muscle which, particularly in the appendages, lie upon the bones and are connected to them. They form the main organs of motion and are familiar in general appearance. The number of separate muscles is large, and, to a small extent, variable. They are commonly arranged in pairs, so that the work of one is directly the contrary of that done by the other: one muscle bends the joint, its antagonist straightens the part; one twists the head towards the right, its opponent reverses the motion. The large group of muscles connected directly with the skeleton are under the control of the will, and are hence called voluntary muscles. There is, however, another group, surrounding the alimentary canal and other organs, which are not controlled knowingly by the brain, and these are known as involuntary or visceral muscles. Still a third type, found in the heart, are similar in structure to the skeletal muscles, but are also beyond the control of the will, and hence may be said to stand intermediate between the two groups. The visceral muscles are unstriped in structure and are arranged in flat sheets or irregular loose masses; their action is slow and ordinarily repeated at intervals, as may be observed in the so-called peristaltic movements of the intestine by which the food masses are propelled through the length of the alimentary canal. A skeletal muscle is commonly somewhat spindle-shaped, the central portion consisting of a closely packed mass of muscle fibres, connecting at the ends with fibres of white, nonelastic tissue, which are grouped together to form a tough white cord or tendon. These tendons constitute the means by which muscles are attached to the various portions of the skeleton, and at the point of attachment the fibres of the tendon pass into the bone itself, making an exceedingly firm union. Ordinarily such a muscle spans a joint, being attached to the bone above the joint and also to that one below the joint. When in action the muscle has the power of contracting strongly, so as to materially reduce its length, while at the same time the thickness is increased in corresponding degree, since the volume of the muscle remains the same. The result of its contraction is, hence, to alter the position of the bones to which it is attached, as in the case of the familiar biceps muscle of the arm to bend or flex This process The form of the body is determined in gen- the forearm on the upper arm. Since the long axis of the muscle lies nearly parallel to the bones, and the power is applied at a very acute angle, it is evident that the work is done at a great disadvantage; in other words, the real power of the muscle is far beyond its apparent power. The actual power has been found to be equal to more than 200 ounces for a human muscle having a cross-section of one-sixth of a square inch. In general, the force exerted by a muscle is proportional to the number of fibres in a section transverse to the fibres; the extent of the motion, however, increases with the length of the fibres. The direction of the fibres is by no means always coincident with the long axis of the muscle, but may be oblique, in which case the fibres are attached to a tendon running down the side or center of the muscle. In this case an apparently long muscle, such as the gastrocnemius or calf muscle of the lower leg, may be in reality a short thick muscle, with the limited but powerful action of that class of muscles. The powerful working of a muscle is, however, not in the least degree spontaneous; it only results in response to a stimulus. This ordinarily comes to it through the nerve fibres, which are connected to the muscle, but it may also be produced experimentally by heat, pressure, an electric current, or by chemical means. The necessity of nerve connection for normal action in muscles is readily demonstrated by those cases in which paralysis has been caused by accident or disease interrupting the nervous connections. The muscles are healthy and ready to work, but remain passive, since the means of stimulation are interfered with. When contracted a muscle has completed its work; there is in it no tendency to return to the previous form. As soon as the state of active contraction is past the muscle lies inert; here it is that the arrangement of these organs in antagonistic pairs becomes of importance. In response to a stimulus the opposing element contracts and the first muscle is passively stretched to its former length, while the part assumes its first position. The effect of the simultaneous equal contraction of antagonistic muscles is merely to "set" the part to which they are attached in a rigid condition. The various positions of the body are due to the united action of the muscles, which are coordinated by the nervous system. Most characteristic for man is the erect position, in which, on account of the distance of the center of gravity from the ground, the body rests in decidedly unstable equilibrium. It is maintained thus by the action of various sets of muscles in front, behind, and at the sides; these remain in a condition of balanced contraction and keep the joints rigid. But let the control of the nervous system be removed in any way, by a blow on the head or by the action of stimulants, and the muscles cease to act, since they |