144 ROBERT BENNETT BEAN 



the adjacent tooth. The position or size of the blood vessels 

 may determine the precocity of the tooth, just as the greater 

 quantity of pure blood going to the head in the fetus may ac- 

 count for the early precocity of that part. There may be blood 

 vessels to the first molars and median incisors that are larger than 

 those to the other teeth at first, or there may be an initial stimu- 

 lus to these teeth that is greater than to the other teeth. Biting 

 and chewing in the region of the median incisors and first molars 

 is apt to be greater at first than in the region of the other teeth. 

 In the same way the rapid growth of the lungs soon after birth 

 and the closure of the ductus arteriosus and foramen ovale may be 

 explained by the shunting of the blood stream from its fetal 

 course through the foramen ovale and ductus arteriosis to its 

 postnatal course through the right ventricle and pulmonary 

 artery. The activity of the lungs inmiediately after birth sucks 

 the blood through the puhnonary artery and right ventricle that 

 formerly went through the foramen ovale and the ductus arterio- 

 sus to the body, and thus allows the closure of the last two 

 channels. 



The ductless glands with their internal secretions poured into 

 the blood stream play a part in developrtient that is little under- 

 stood, but if the normal effect of the secretions may be inferred 

 from their abnormal effect, we may know more than we think, or 

 understand. I cannot enter here into a review of the literature 

 of the internal secretions, which is enormous, but I wish to pre- 

 sent a few facts that may be relevant. We may infer from 

 recent work that the hypophysis influences the growth of the 

 bones, and there is some indication of the antagonistic action of 

 the sex glands and the hypophysis, which may account for the 

 retardation of the growth of the bones (stature) after puberty. 



The growth of the sex glands is irregular after birth, according 

 to Jackson and Hatai, and if this irregularity in their development 

 bears any relation to the periods of acceleration in stature, we 

 may have a causal relationship. 



The thyroid influences growth, because hypothyroidism pro- 

 duces cretinism and hyperthyroidism produces rapid differen- 

 tiation with irritability of the nervous system, when either occurs 



