A PERFECT LUBRICATING SYSTEM 85 



troops ; in the deeper stratum they form single files, as if 

 they were advancing towards the underlying bone spaces ; 

 in the more superficial stratum they are compressed into 

 ranks or rows, parallel to and advancing towards the 

 rubbing surface. As they approach towards the surface, 

 the cartilage-builders become flattened and the outlines of 

 their bodies blurred. To the naked eye the rubbing 

 surface seems perfectly smooth, but under the microscope 

 we can see minute pits on it. When we examine such a 

 pit with care we can usually find in it some trace of a 

 ground-down cartilage-builder. Those surface rows of 

 builders are advancing to make good the waste entailed 

 by the rubbing of one articular plate on the other. We 

 can see any day the same kind of thing happening in our 

 skin ; in every movement of our bodies our under- 

 garments rub off the dried mummified remains of 

 epidermis which is being shed by the skin. But there 

 is this difference : when a cartilage-builder is sacrificed 

 on the altar of duty, it does not become withered and 

 dry like the scales of the cast-off scarf skin, but 

 becomes soft and slippery ; its body is turned to 

 synovia — the oil or lubricant of joints. Here, then, 

 is an easy way not only of making good the wear 

 of a joint, of both shaft and bearings, but of keeping 

 constantly between them a thin uniform film of lubricant 

 — the ideal which engineers dream of but cannot attain. 

 Yet Nature has worked the ideal out in the joints of our 

 bodies by the simple method of using cartilage-builders 

 to make good the wear of the joint surface, and then 

 when their working days are over dissolving their bodies 

 to form a lubricant ! 



We must not overlook certain other difficulties con- 

 nected with joint construction which Nature cleverly 

 surmounted at the same time. In a perfect system the 

 supply of lubricant must be in proportion to the amount 

 of work done. If there is more work done a greater 

 supply of oil will be necessary. In Nature's system the 

 supply of oil is automatic ; the more the joint surfaces 

 move on each other, and the greater the pressures brought 



