PATHOLOGICAL ANATOMY AND HISTOLOGY 559 



acute infections and intoxications must be thoroughly understood to appre- 

 ciate their role in health and disease. 



Margin of Safety in Parathyroid Deficiency. It has been amply illus- 

 trated in the experimental work that the sudden and complete deprival of 

 the parathyroid tissues in animals leads to the development of marked 

 symptoms with convulsions and death (tetany). Such destruction of the 

 parathyroid may be accomplished by excision, or by the crushing of tissues 

 accompanied by hemorrhage. It has been estimated that at least three- 

 quarters or more of the functioning parathyroid tissue must be destroyed 

 to bring about these severe manifestations (Thompson and Leighton), and 

 it is probable that the same quantitative conditions hold for the spontane- 

 ous development of the manifestations of parathyroid deficiency. It must 

 be recognized, however, that it is likewise possible to have minor lesions 

 occupy one or more of the parathyroid glandules, without having our atten- 

 tion attracted to the injury in the absence of specific symptoms. This has 

 been observed in cases where tumor has occupied one or more of the para- 

 thyroids (Thompson (c), Koenigstein) , in which during life no evidence 

 of functional insufficiency has made its appearance. Similar observations 

 have been made in cases where hemorrhage has occurred into the parathy- 

 roids, but has not completely destroyed their activity (Thiemich (c), 

 Haberfeld). 



Manifestations of Slowly Developed Parathyroid Deficiency. 

 Thompson and Leighton have shown that when the parathyroid function 

 has been slowly disturbed the manifestations are not those of acute tetany, 

 but more of the nature of nutritional disturbances with trophic change. 

 Erdheim has commented upon the peculiar functional disturbances asso- 

 ciated with enamel defects, fracture of teeth, and occasional gastrostoma- 

 titis, where partial and progressive parathyroid lesions were present. Mac- 

 Callum has made similar observations, the acute tetany giving place to a 

 stuporous condition, which lasted several days before terminating in death. 

 These observations have been confirmed by Thompson and Leighton, who, 

 furthermore, have added that where the chronic symptoms trophic in na- 

 ture arise, there is not uncommonly evidence of greatly diminished resist- 

 ance to infection. 



Anomalies of the Parathyroids 



Variations in Position. A considerable variation in the position, 

 number and size of the parathyroids has been reported. 



Variations in Man. As normal for the human, we may take it that 

 there are two pairs of these glandules, a set on each side, consisting of a 

 superior and inferior body in close relation to the lobe of the thyroid. The 

 superior parathyroid is most constant in its position, occupying a place 

 along the posterolateral border of the thyroid, and a short distance below 





