ERUPTION OF THE PERMANENT TEETH 143 
of the Filipino boys may illustrate this. Take the lower teeth, 
for instance. In the median series the median incisors are 
precocious, hence the lateral incisors are relatively backward, 
hence the canines are relatively precocious, hence the median 
premolars are relatively backward, and hence the lateral pre- 
molars are relatively precocious. In the lateral series the first 
molars are relatively precocious, hence the second molars are rela- 
tively backward, and hence the third molars are relatively pre- 
cocious. The alternation is also true for the lateral series of the 
upper teeth where the first molars are backward, the second molars 
are precocious and the third molars are backward, which is not 
only an alternation of adjacent teeth, but also of the similar 
teeth of opposite jaws, because the lower first molars are pre- 
cocious, and the upper first molars are backward, the lower second 
molars are backward and the upper second molars are precocious, 
and the lower third molars are precocious and the upper third 
molars are backward. 
Racial differences in growth also fall within the law of alterna- 
tion in development. It is evident from this and other studies 
already published or at present under way that the Filipinos 
mature later than the Europeans in morphologic form, especially 
of the face, head, nose, etc., or never reach the state of the mature 
European, yet the Filipinos mature earlier than the Europeans 
(Ann Arbor Germans and Americans) in stature and in the erup- 
tion of the teeth. Does the early development of the teeth and 
stature in the Filipinos cause the late maturity of the head and 
face, and the early development of the head and face of the Euro- 
pean cause a late development of the teeth and stature, or are the 
differences incidental, or caused by other factors? 
A presentation of the supposed causes of alternation in develop- 
ment would be incomplete without suggesting the influence of 
mechanical factors and the internal secretions. The alternation 
in development of the teeth may be produced by a more rapid 
growth of one tooth than another due either to an initial stimulus, 
or to a better blood supply. The adjacent tooth may be crowded 
back by the precocity of the one that develops first and the 
substances used in the building of the latter delay the growth of 
