Page:Popular Science Monthly Volume 33.djvu/504

488 laid and then kept in repair. Londoners find asphalt the best pavement for all but the very heaviest traffic, in spite of its being very slippery in wet weather. The advantages far outweigh this one disadvantage. Horses can draw much heavier loads than on Belgian block, with less noise, while they are the cleanest pavements known. Those called asphalt pavements in America are a poor imitation of what our English brethren enjoy. Intelligent, honest city government, in a word, will give us health as well as increased business facilities.

Jarring is an equally hurtful influence of city life that has not received the attention it deserves. Combined with the two preceding, it completes a formidable trio. Very few realize the fact that we who were designed to tread upon soft Mother Earth have become a race of dwellers upon rocks and stones. In walking, the jar of the fall of our one hundred and fifty pounds comes entirely upon the heel, since it first strikes the ground. The ball of the foot and the instep serve only to raise us for another downfall—small, it is true, but equal to the weight of our bodies falling through one half to one inch in a little less than one second. This shock would be sudden and unbearable but for the arrangement of the bones, muscles, and ligaments of the lower limb. The chief elastic distributing springs are the mass of muscles on the front of the thigh and that on the front of the leg. These deaden the shock much as two great India-rubber bands. The ankle and hip joints help but little, while the curves of the spine and the disks of cartilage between the vertebrae aid a great deal in lessening the impact of the body with the ground.

This shock in ordinary walking is less than if the body be raised one half or three quarters of an inch on the toes, and then suddenly let fall upon the heels, since the limb which is put forward is somewhat like the spoke of a wheel, if we imagine a wheel consisting of an axle and spokes alone. The brain bears almost the same relation to its containing bony case, the skull, that the ball does to the cup, in the old-fashioned cup-and-ball, where the ball is tossed into the air and caught in its cup with a sharp shock.

If any one doubts that there is a distinct and decided jar of the brain with each step, let him walk a hundred yards when the brain is slightly over-sensitive from a bad cold or headache, and he will observe the pain each step causes. Or, more scientifically, let him place (as I did recently) a pedometer inside his hat, and it will register every time his heel strikes the ground.

Fortunately the brain, in health, does not perceive these slight jars to its own substance, and interpret them as pain. Nature provides one more anatomical precaution against jarring by slinging up the brain in its spherical hammock, the dura mater. Now, in many people, the ill effect of these thousands of slight daily