ERUPTION OF THE PERMANENT TEETH 123 



3. Periods of acceleration and retardation in growth 



Growth occurs in waves. A period of acceleration is followed 

 by a period of retardation. The periods occur at different times 

 in the different sexes and races. 



The first period of acceleration of which we have any record 

 occurs between the ages of 6 and 10 years, after which there is a 

 retardation followed by another acceleration about the age of 13 

 to 15. These periods may be of interest in relation to the erup- 

 tion and decay of the teeth. 



Disregarding the first and second periods of rapid growth, of 

 which we have no record here, it may be seen that the third 

 period of growth begins at about the age of 7 years and continues 

 until about the age of 10, being most rapid from 7 to 8, and at 

 the age of 10 years the third period of growth begins. 



The third and fourth periods of rapid growth are earlier for 

 the girls than for the boys and the fourth period of rapid growth 

 is shorter for the girls than for the boys. The result is that the 

 girls become larger than the boys between the ages of 7 and 15, 

 and remain so until the fourth acceleration sets in for the boys, 

 when they outstrip the girls in stature and remain taller there- 

 after. 



The stature of the Filipinos is less than that of theGermansand 

 Americans and this becomes more evident after the age of 14 

 years. 



The stature of the Igorot boys is less than that of the Filipino 

 boys and girls except at the ages of 7 to 8 when it is greater than 

 that of the Filipino boys, and at the age of 20 when it is greater 

 than that of the Filipino girls. 



The Igorot boys attain their growth later than either the Fili- 

 pino girls or the Filipino boys, but earlier than the German or 

 American boys and girls. 



The four groups may be arranged in order of precocity of 

 acceleration periods as follows: 1, Filipino; 2, Igorot; 3, German; 

 4, American. The acceleration periods of the German begin 

 earlier than those of the American but the ultimate stature is 



