IN HYGIENIC PHYSIOLOGY. 147 



joints is done by the muscles on the front part of the thigh, 

 that draw up the knee-pan with the tendon attached to it. 

 This is using the principle of the toggle-joint in pressing up- 

 ward. It is also sometimes used in pressing downward. In 

 crushing any thing with the heel, we give great force to the 

 blow on the principle of the toggle-joint, by flexing the knee 

 and straightening the limb as we bring down the heel upon the 

 thing to be crushed. In pushing any thing before us, we bend 

 the elbow as preparatory to the act, and then thrust the arm 

 out straight, thus exemplifying the toggle-joint. The horse 

 gives great force to his kick in the same way. The great 

 power exerted by beasts of draught and burden is to be re- 

 ferred very much to the principle of the toggle-joint. When a 

 horse is to draw a heavy load, he bends all his limbs, especially 

 the hinder ones, and then as he straightens them, he starts the 

 load. In this case the ground is the fixed block of the mechan- 

 ism, the body of the horse to which the load is attached is the 

 movable one, and his limbs are so many toggle-joints. By this 

 application of the principle, we see draught horses move very 

 heavy loads." HOOKER'S Physiology. "So (admitting fable to be 

 fact), when the farmer, in answer to his petition for assistance, 

 was commanded by Hercules to exert himself to raise his wagon 

 from the pit, he placed his shoulder against the wheel, and 

 drawing his body up into a crouching attitude, whereby all his 

 joints are flexed, and making his feet the fixed points, by a 

 powerful muscular effort, he straightened the toggle-joints of 

 his limbs, and the wheel was raised from its bed of miry clay. 

 His horses at the same moment extending their joints, the 

 heavily laden wagon was carried beyond the reach of further 

 detention. " G-BISCOM. 



8. What class of lever is the foot when we walk ? 



In the first stage it is clearly the second class. (See Physi- 

 ology, Fig. 18.) The fulcrum is the ground on which the toes 

 rest ; the power is applied by the gastrocnemius muscle (see 

 Fig. 14, ft) to the heel ; the resistance is so much of the weight 

 of the body as is borne by the ankle-joint of the foot, which of 

 course lies between the heel and the toes. 



