THE THYEOID GLAND AND ITS DISEASES 219 



and its qualities may offer valuable indications of the capacity of fhe 

 thyroid cell for normal storage. The colloid in fact may be the product 

 of a storage phase, which preceded the examination of the gland by a 

 considerable period of time, since it is necessary to explain the resorption 

 of this material only under the conditions where the normal secretory 

 activity of the gland is insufficient to meet the functional demands. Ac- 

 cordingly, also, lack of colloid in the gland does not necessarily mean 

 depression of the gland activity below the normal rate at the time of 

 observation, though it probably does mean there is such a depression of 

 physiological efficiency, or has been at some previous period, and either 

 that the gland has not risen above the level of secretory rate needed for 

 direct export, or that there has been a failure of the normal mechanism 

 of regulation. 7 ' 



Embryologic Evidence of Primitive Secretory Ducts. Bensley's view 

 that the secretion is poured directly into the blood vessels and lymphatics 

 is strongly supported, up to a certain point, by Norris's embryological 

 studies, to which reference has already been made. According to these 

 studies the intraglandular spaces, which he has found in the developing 

 gland, represent ancestral lumina. These communicate with the periphery 

 of the gland anlage in the course of development, and become invaded 

 with connective tissue, blood vessels, and lymphatics. The follicles de- 

 velop through the formation of cavities in their walls, which are lined 

 by a single layer of cells. He, therefore, suggests that the perifollicular 

 spaces in the mature gland represent the ancestral himina, and that one 

 would naturally expect the secretion to be directly poured into them; 

 hence it may be unnecessary, as Bensley has done, to postulate a reversal 

 in polarity. 



Very recently, however, I have found that the reticular apparatus 

 moves actively from one pole of the thyroid cell to the other under quite 

 normal conditions which I believe to be the visible expression of changes 

 in the direction of secretion. As has already been mentioned it generally 

 occurs in the distal part of the cell between the nucleus and the follicular 

 cavity (Fig. 7). Its distance from the lumen is usually about the same 

 in individual follicles. Occasionally the position is completely reversed 

 so that it is found on the other side of the nucleus. This reversal may 

 occur sharply in one cell only, or a cross section of a follicle may show 

 successive stages in proximal migration. Migration may also take place 

 in the opposite direction, all the reticular material moving toward the 

 follicular cavity. These changes seem to be more frequent when the epi- 

 thelium is high and columnar and the cells are perhaps more active. An 

 examination of other glands indicates some correlation between the posi- 

 tion of the reticular apparatus and secretory polarity. When the secre- 

 tion has definite direction it is indicated by the position of the reticular 

 apparatus between the nucleus and the discharging pole of the cell (acinar, 



