y., 



488 THE POPULAR SCIENCE MONTHLY. 



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 pave- 

 ments 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 pre- 

 ceding, 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 for- 

 ward 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 reg- 

 ister 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 pro- 

 vides 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 con- 



