322 The Outline of Science 



provision which obviates this: the teeth do not fit tightly in the 

 sockets. They are "packed" in with a material that lessens the 

 shock of the daily grind. 



A special regiment of the cells which make up the body is 

 told off to see to this business of the teeth, and our wonder in- 

 creases when we see these strange microscopic, unconscious "bone- 

 builders." They have, in the baby, to select, atom by atom, the 

 cement and dentine and enamel which (in other forms, of course) 

 somehow exist in the food of the blood-stream. They have to 

 build the stuff into structures of which our artificial teeth are very 

 clumsy imitations. They have to do this at the right time to 

 wait until suckling is over and eating begins. Then they have 

 an even more difficult problem to face. The jaws of the adult 

 will be much larger than the jaws of the young, and, naturally, it 

 is not possible to alter these solid structures of enamel and den- 

 tine. So the bone-builders absorb the greater part of the first set 

 of teeth, the "milk-teeth," and meantime prepare a new set under- 

 neath them. The cast tooth which your child shows you is, as a 

 rule, a mere shell. The microscopic bone-builders have re-ab- 

 sorbed the material. 



Yet the teeth, with all their wonders, may be among the 

 doomed structures of the body. Some authorities believe that 

 they will gradually drop into the class of vestigial organs, like the 

 hair, though they will give a vast amount of trouble as they grow 

 weaker. Their purpose is to break up the food into smaller par- 

 ticles, and in modern civilisation this is done in the preparation 

 and cooking of the food. So the teeth are already going. In 

 ancient skulls and among savage peoples the teeth are often much 

 worn away by sheer hard work; in conditions of civilisation 

 much-worn teeth are rare. The jaws have not the hard work 

 they once had ; they therefore get a smaller supply of blood, and 

 the teeth grow weak and less numerous. Normally we have 

 thirty-two teeth, but in many people the so-called "wisdom teeth" 

 (which might very well be called unwisdom teeth, as they are 



