6 



Scientific Proceedings (85). 



Impairment of normal nutritive and endocrinic influences, by 

 subtraction, has been induced by extirpation of various glands in 

 albino rats. There were no effects on dentition after thymectomy, 

 thyro-parathyroidectomy, and castration; deficient calcification 

 of the teeth (incisors) followed parathyroidectomy. 



Modification of normal nutritive and endocrinic influences, 

 by addition, has been induced by feeding various glands to white 

 rats. Dental calcification appeared to be (a) regularly decreased 

 by oral administration of lymphatic, salivary, or thyroid, gland; 

 (b) regularly increased by oral administration of testicle; and (c) 

 wholly unaffected by oral administration of corpus luteum, para- 

 thyroid, pineal, pituitary, spleen, suprarenal, or thymus. 



There were no effects on the general condition or dimensions 

 of the teeth in any of the foregoing experiments. 



Physiological variation in the composition of the teeth, in 

 albino rats, is relatively slight and not great enough to account 

 for any of the findings that were indecisive. 



The well-known chemical methods we have employed were 

 found to be adequate to detect significant chemical differences in 

 dentition. Various results of uncertain import have not been 

 due, at any time, to deficiencies in the analytic procedures as such. 



Underlying all our experiments on the effects of internal 

 secretions is the assumption that chemical changes may take 

 place, in developing enamel, through the influence of substances 

 that originate outside of, and enter, or superficially affect the cells 

 involved in the production of enamel. If this assumption is un- 

 warranted, it is obvious that internal secretions can have no direct 

 chemical effect on the production or condition of enamel. If this 

 assumption is incorrect, internal secretions can have, at most, only 

 indirect effects on the development of enamel. 



That our assumption in this general regard is correct, however, 

 is shown by the fact that trypan blue, after its intraperitoneal 

 injection into young rats, rabbits, and dogs, passes freely into 

 the enamel of developing teeth, where the blue pigment seems to 

 remain indefinitely; it does not pass from pulp through dentin 

 into enamel of fully erupted teeth. (These particular facts were 

 demonstrated at the meeting of the Society.) 



That our assumption in this general regard is justified is shown, 



