540 ADDENDA. 



His system, though not really new, is very simple, nnd for outsiders 

 veiy useful. 



" Sometimes at 0, always at 10 years old, a dark yellow streak begins 

 to appear at the upper end of the groove in the centre of the upper corner 

 tooth." 



This streak at first is not more than ^ inch in breadth or length, but 

 increases in length each year about |, until it reaches the lower end of 

 the tooth about the age of 20. 



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