506 E. V. COWDEY 



Mode of Secretion. True secretion antecedents remain to be dis- 

 covered. We have convincing evidence that the glands do form some- 

 thing since removal, or mere ligation of their blood vessels, causes tetany 

 and other characteristic symptoms, which are to some extent relieved by the 

 injection of parathyroid extracts. Young animals are more susceptible 

 than old ones and certain species more than others. 



Preparations made by Fano's new (1920) cobalt and silver nitrate 

 method reveal the fact that the reticular apparatus exhibits great varia- 

 bility in its cytoplasmic location, from which we may conclude that the 

 cells are not definitely polarized for secretion in one direction (see thyroid 

 section). Only when the parathyroid cells become grouped in clumps is 

 there an assumption of secretory polarity as indicated by the reticular appa- 

 ratus taking up a position between the nucleus and the discharging pole. 



The ground substance in the cell, in which we can see no structure!, is 

 the active agent in almost all vital manifestations, including secretion. It 

 is not homogeneous, however, because heterogeneity is prerequisite to 

 activity. It is organized so as to permit of combination and isolation of 

 chemical reactions, just as a factory is organized in space; but the mechan- 

 ism of the organization in the cell is almost wholly unknown. Indeed, it 

 cannot be too strongly emphasized that the absence of visible secretion 

 antecedents does not mean that they do not exist. This is one of the limi- 

 tations of anatomical evidence. In order to touch on fundamental vital 

 processes, we must extend our views to include a study of the morphology 

 of the nltramicroscopic. 



Functional Relation to Thyroid. Some investigators are of the opin- 

 ion that the parathyroids are very closely related anatomically and physio- 

 logically to the thyroids, especially to the intervesicular cells already re- 

 ferred to in the section on the thyroid. Changes in the parathyroids, char- 

 acterized by the formation of vesicles containing colloid after thyroidec- 

 tomy, have been frequently described, though Vincent has recently ex- 

 pressed doubt regarding them. 



The chief differences between the two glands are as follows: (1) In 

 congenital atrophy of the thyroids the parathyroids are usually well de- 

 veloped, indicating a different manner of growth. Jackson has found that 

 their growth energy exceeds that of the thyroid. (2) According to Ott's 

 observations, as yet unconfirmed, extracts of the two have totally different 

 physiological effects (citation from Schafer). (3) Their removal pro- 

 duces different symptoms, which even show a tendency to be antagonistic. 

 (4) lodin in any considerable amount is absent from the parathyroids. 

 The claims which have been made, to the effect that thyroidectomy is fol- 

 lowed by enlargement of the parathyroid glands and the deposit of colloid 

 substance within them, are very difficult to substantiate. 



Variations. From the cytological point of view, the parathyroid 

 glands have been so neglected, owing perhaps to the difficulty of studying 



