74 THE ENGINES OF THE HUMAN BODY 



end rubs against the tibia in the knee-joint; had the 

 growth discs been placed on the ends they would have 

 been exposed to constant disturbance. And yet the 

 growth discs are sometimes disturbed. When children 

 are wrongly fed the regular and orderly warfare in the 

 growth discs no longer goes on, and the child becomes 

 " rickety " and its growth stunted. Then there is another 

 disturbance which may take place ; the cartilage-builders 

 of the growth discs, for some reason we do not yet under- 

 stand, go on strike ; the bone-builders, while they keep 

 on laying down surface layers and thus increasing the 

 thickness of the bone, can make no headway at the 

 growth discs, and hence the bones laid down are very 

 short, thick, and stumpy. The boys and girls who suffer 

 from this condition grow into strong, thickly set dwarfs, 

 examples of which can be met with in the streets of all 

 towns and cities. The disturbed growth from which they 

 suffer is called Achondroplasia, which means a lessened 

 growth of cartilage. It is this kind of dwarf which plays 

 the part of gnome in fairy stories ; in olden times kings 

 kept them as jesters. In some children a blight falls on 

 the bone-builders as well as the cartilage-builders of the 

 entire body ; the boy or girl who is afflicted with this 

 condition remains childish in height and appearance as 

 long as life lasts. Then there is another very marvellous 

 transformation which may overtake growth discs. Usually 

 it occurs just when manhood or womanhood is being 

 reached ; suddenly the cartilage- and bone-builders be- 

 come excessively active, and in the course of three or 

 four years the sufferers shoot up into giants. In recent 

 years medical men have made discoveries which explain 

 this growth madness. It is very clear that there must be 

 some way of regulating the rate of growth in all the 

 cartilage discs, otherwise the discs of one bone might 

 grow too much while those of its neighbour did not 

 grow enough. Now, all the bone-builders are given a 

 very liberal supply of blood for their nourishment ; 

 bones are permeated with a fine meshwork of vessels, 

 and in the blood are certain substances — we may even 



