ERUPTION OF THE PERMANENT TEETH 153 



arc! for each group of individuals in relation to the eruption of 

 each tooth. The ages given are the ages at which the teeth nor- 

 mally appear. If the teeth appear earlier in any individual, that 

 individual is precocious, and if later, backward. 



The physiological standard may be utilized to greater advan- 

 tage with increasing age, because the racial and sexual differences 

 increase with age. A word as to one way in which such a table 

 may be of use. Take a German girl of 10 years, and all the in- 

 cisor teeth, the first molars, premolars and canines may be 

 erupted, whereas a German boy may not have all these teeth 

 erupted until 11 years of age, yet at 11 years he may be at the 

 same physiological standard as the girl at 10 years. Should 

 either one have all the teeth mentioned erupted at the age speci- 

 fied there would be evident precocity. In like manner evident 

 backwardness may be determined. 



The teeth are more convenient and more exact as a means of 

 determining the physiological standard than stature, or weight, or 

 the growth of the bones, or secondary sexual characters, etc., and 

 they 7nay be of greater value than any other means that can be 

 utilized. The teeth can be seen, recognized and counted by 

 almost anyone after a little experience, and they are either pres- 

 ent or absent, therefore very definite. 



Precocity in the eruption of the permanent teeth is a sign of 

 hyper-morphism, and hyper-onto-morphs are epitheliopaths, who 

 are especially susceptible to diseases of the alimentary canal, the 

 lungs and the central nervous system, therefore precocious chil- 

 dren should be shielded from injuries to the susceptible organs. 



Backwardness in the eruption of the permanent teeth is a sign 

 of hypo-morphism, and hypomorphs should be shielded frorii 

 injuries to their susceptible organs. 



THE SCHOOL GRADE AND THE TEETH 



The modal grade, or the grade that has the greatest number of 

 individuals at each age, varies little with sex but the Germans are 

 about one year behind the Americans. This corresponds with the 

 backwardness of the Germans in the eruption of the permanent 

 teeth, and indicates a correlation of mental and dental develop- 



