THE SKELETON 379 



against a fixed point, the fulcrum, in order to raise a certain weight. A 

 seesaw is a lever; here the fulcrum is in the middle, the weight is at one 

 end, and the power to lift the weight is applied at the other end. There 

 are three classes of levers, named according to the position of the fulcrum. 



In the first class, the fulcrum lies between the weight and the power; 

 the seesaw is an example of this. The best example in the human body, of 

 a lever of the first class, is seen when the head nods. Here the fulcrum is the 

 vertebra known as the atlas; the power is the muscles of the neck attached 

 to the back of the skull and to the spine ; the weight is the front part of the 

 head. When one keeps the head erect, this lever is used; the nodding 

 head when one is sleeping shows this plainly. 



A lever of the second class has the fulcrum at one end, and the weight 

 between it and the power; when we rise on our toes, we use this kind of 

 lever. Try to explain this by referring to a skeleton of a frog or of man. 



In a lever of the third class, the fulcrum is at one end, with the power 

 between it and the weight. This is the kind of lever seen most frequently 

 in the human body. The flexing (drawing up) of the lower leg or the fore- 

 arm is an example of the use of this kind of lever. In such a lever, a wide 

 range of movement is obtained. 



Sprains. — A sudden strain or twisting in the region of a joint may 

 result in the pulling out or tearing of the ligaments or tendons of that 

 joint. Such an injury may be recognized by the sudden swelling in that 

 region, followed by great pain. A cure of the sprain is effected only by 

 nature's own remedy, complete rest. For immediate relief hot water 

 applications, followed by arnica or some liniment, are best; a tight bandage 

 should be applied at once and a doctor called as soon as possible. 



Dislocations. — The bones of a joint may be accidentally forced apart. 

 Such a separation is called a dislocation and is known by the intense pain 

 which follows any attempt to move the joint. There is often considerable 

 swelling of the affected part; the bone may even protrude. A physician 

 should be called at once so that the bone may be slipped into place again. 

 Hot or cold water applied to the joint and rest in a comfortable position 

 should be given until the doctor comes. 



Fractures. — A break or fracture usually occurs in one of the long bones 

 of the body. The clavicle or collar bone (easily felt in the front part of 

 the shoulder below the neck), because of its exposed position, is most 

 frequently broken. The immediate treatment for fracture is rest in a 

 comfortable position; cold water applications may relieve the pain. Send 

 for a doctor at once. To heal a fracture, it is necessary to bring the two 

 broken ends of the bone together, and hold them so that they will grow 

 together or knit; for this purpose splints are often employed. 



