50 R. E. BENSLEY 



conceivable, of course that the droplets of colloid are of two sorts, 

 those destined for the follicular content, and those on their way 

 to the base of the cell for secretion into the vascular channels of 

 the gland. Opposed to this assumption is the fact that in entire 

 glands, in the cells of which there is an abundance of the basal 

 vacuolar substance there may be found not a single droplet of 

 colloid of the dense type, and that the free poles of all the 

 cells may be wholly free from products of secretion except where 

 the crystals, of protein nature, demonstrated in a former article, 

 project into this pole. Furthermore, in hyperplasia of long 

 standing, in which there is practically no intrafollicular colloid, 

 a large content of the new secretion in the form of small vacuoles 

 distributed throughout the outer pole of the cell, may be present. 



We are therefore forced to accept the third hypothesis which, 

 physiologically considered, is the more attractive, inasmuch as it 

 permits of harmonizing the various facts under a single hypothe- 

 sis, namely that the secretion collected in the outer pole of the 

 thyroid cell is destined to direct transport into the vascular chan- 

 nels, and that the thyroid cell represents a true reversal of 

 polarity in accord with its endocrine function. 



In addition to the facts mentioned above which point strongly 

 to the correctness of this hypothesis, it may be pointed out 

 that in exocrine glands fat droplets which are deposited in the 

 secreting cells practically always make their appearance at the 

 anti-secretory pole of the cell; this is the case in the pancreatic 

 cells and in the chief cells of the gastric glands. The location 

 of the fat deposits in the thyroid gland also is at the pole which 

 according to the hypothesis here supported is the anti-secre- 

 tory pole of the cell, namely the free end of the cell next the 

 colloid. 



We may assume therefore that the thyroid gland as all physio- 

 logical and clinical experience indicates, prepares and secretes 

 into the vascular channels of the gland a secretion, and that this 

 secretion is formed in the outer pole of the cell, and excreted from 

 it directly under normal conditions of functioning without passing 

 by the indirect route through the follicular cavity. 



c 



