PAKATHYKOID GLANDS 615 



they played a considerable part in the production of the marked emacia- 

 tion and cachexia that characterized these animals. Erdheim made 

 histological studies of the teeth in such experimental rats, and found 

 that the trophic disturbances in the teeth appeared quickly after the 

 injury to the parathyroid glands. He was able to demonstrate (1) a 

 faulty calcification of the dentin and (2) hypoplasia of the enamel. 



A comprehensive study of the finer histological changes in the teeth 

 in experimental tetany in rats has been made by Toyofuku (1911), work- 

 ing under Erdheim's direction. He has described in detail the faulty 

 calcification of the dentin, and the peculiar changes in the enamel 

 that are observable after removal of the parthyroid glands of these 

 animals. 



Erdheim himself (1911) succeeded, by performing autotransplanta- 

 tion of parathyroid glands immediately after extirpation, in producing 

 a temporary status parathyroprivus, which was again abolished after 

 the graft had taken. A most interesting result of this experiment was 

 observed. A narrow strip of dentin, poor in calcium, corresponding to 

 the period of status parathyroprivus, appeared and persisted. Erdheim, 

 by this and similar experiments, sought to prove that teeth undergoing 

 development at a time when a status parathyroprivus occurs show per- 

 manent enamel defects. 



Stimulated by these interesting researches of Erdheim on experimental 

 tetany in rats, L. Fleischmann (1907-9) made exhaustive studies of the 

 trophic changes in the teeth of children in rickets and in tetany. The 

 findings in rickets, though very important, do not concern us here, but 

 in cases of infantile tetany, along with the dentin changes due to rickets, 

 he found characteristic changes in the enamel due to the tetany. These 

 changes consist in defects in the enamel covering of teeth true hypo- 

 plasias of the enamel. They take the form of little pit-like depressions, 

 arranged often in rows extending horizontally across the tooth. Some- 

 times a single row of such pit-like enamel defects is seen ; sometimes two 

 or three parallel rows superimposed one above another running around the 

 whole circumference of the tooth. Fleischmann further demonstrated 

 that persons who have had tetany in the first or second year of life, that 

 is at a time when certain of the teeth develop (most often the first molars, 

 the medial upper incisors, the canines, and the inferior incisor teeth), 

 carry throughout life typical enamel defects, whereas, when the tetany 

 occurs between the third and fifth years of life, the enamel defects are 

 found on the second bicuspids, the second molars, and the wisdom teeth. 

 Fleischmann emphasizes the fact that it is not single teeth that show 

 these hypoplasias of the enamel; they are in evidence on all the teeth 

 that happen to belong to the developmental period of the time when the 

 tetany occurred. He asserts that these enamel defects have nothing to 

 do with rickets, as was formerly supposed, but are wholly due to the 



