Sensation 83 



if the growth is so slow that the envelope 

 cannot adjust itself to the new conditions. 

 But where growth is active, the envelope yields 

 before the growing nerve, until an equilibrium 

 is attained, with the result that a new organ is 

 formed. In case a partial break in the envelope 

 is made, renewed growth, finally gaining the 

 upper hand, keeps the nerve encased in 

 the envelope. A tooth seems to me to have 

 such an origin. The nerve, in its effort to emit 

 its sex products, presses against the skin and 

 partially breaks through. The skin hardens 

 over the injured part and the tooth results, 

 which holds the nerve in. The troubles of 

 children in teething are due to the conflict of 

 the nerve forces and the growth forces. In the 

 end the latter conquer, and then an equilibrium 

 is attained with a passive nerve. 



On the face of things, this may seem an inad- 

 equate explanation, because teeth appear to 

 come because they are useful, and the result of 

 adjustment rather than a mere effort of sex 

 products to free themselves. But it should 

 be remembered that teeth in lower organisms 

 are not necessarily useful organs. They often 



