We also see that the weight scale moves at nine times the speed of the sugar scale. Now it often happens that Nature wants to increase, not the power, but the speed with which a load is lifted. In that case the "sugar scale" is placed at the long end of the beam and the "weight scale" at the short end; it then takes a 9-lb. weight to raise a single pound of sugar, but the sugar scale moves with nine times the speed of the weight scale. Nature often sacrifices power to obtain speed. The arm is used as a lever of this kind when a cricket ball is thrown. Nothing could look less like a pair of scales than a man's head or skull, and yet when we watch how it is poised and the manner in which it is moved, we find that it, too, acts as a lever of the first order. The fulcrum on which it moves is the atlas--the first vertebra of the spine (Fig. 2). When a man stands quite erect, with the head well thrown back, the ear passages are almost directly over the fulcrum. It will be convenient to call that part of the head which is behind the ear passages the _post-fulcral,_ and the part which is in front the _pre-fulcral._ Now the face is attached to the pre-fulcral part of the lever and represents the weight or load to be moved, while the muscles of the neck, which represent the power, are yoked to the post-fulcral end of the lever. The hinder part of the head serves as a crank-pin for seven pairs of neck muscles, but in Fig. 2 only the chief pair is drawn, known as the _complex_ muscles. When that pair is set in action, the post-fulcral end of the head lever is tilted downwards, while the pre-fulcral end, on which the face is set, is turned upwards. [Illustration: Fig. 2.--The skull as a lever of the first order.] The complex muscles thus tilt the head backwards and the face upwards, but where are the muscles which serve as their opponents or antagonists and reverse the movement? In a previous chapter it has been shown that every muscle has to work against an opponent or antagonist muscle. Here we seem to come across a defect in the human machine, for the _greater straight_ muscles in the front of the neck, which serve as opposing muscles, are not only much smaller but at a further disadvantage by being yoked to the pre-fulcral end of the lever, very close to the cup on which the head rocks. However, if the _greater straight_ muscles lose power by working on a very short lever, they gain, in speed; we set them quickly and easily into action when we give a nod of recognition. All the strength or power is yoked to the post-fulcral end of the head; the pre-fulcral end of its lever is poorly guarded. Japanese wrestlers know this fact very well, and seek to gain victory by pressing up the poorly guarded pre-fulcral lever of the head, thus producing a deadly lock at the fulcral joint. Indeed, it will be found that those who use the jiu-jitsu method of fighting have discovered a great deal about the construction and weaknesses of the levers of the human body.