33 



HUMAN PHYSIOLOGY 



Between eighteenth and twentieth month the four 

 canines. 



Between twenty-fourth and thirty-fourth month the four 

 smaller outer molars. 



Between the age of 4^ and 5 years, the first four large 

 permanent molars appear. 



2. CHILDHOOD 



Childhood extends from the first dentition to puberty. 

 During this period the physiological functions are about the 

 same as in the adult human being, except that metabolism 

 is relatively greater than in the adult, as already explained 

 (see page I 18), and that the sexual functions are not present. 

 The second dentition takes place during childhood. It 

 begins during the seventh year and extends to the fifteenth 

 year. The temporary teeth are replaced by the permanent 

 set and four new large molars are added. Between the 

 ages of eighteen and twenty-five, and sometimes still later, 

 the last molars, the wisdom teeth, are finally developed. 



The following table shows the changes in the length and 

 weight of the body at different ages : 



3. PUBERTY 



Puberty is the period of sexual maturity, which begins at 

 the age between fourteen and seventeen. It is characterized 



