THE ANATOMY OF THE THYROID GLAND 195 



the vessels, and on the other hand into the folhcular cavity, whence 

 it eventually passes through the follicular wall to reach the vessel. 

 It is in the course of the latter flow that the colloid appears and 

 its volume is dependent upon the rate of flow. 



The question arises as to whether or not the colloid may serve 

 for the storage of secreted materials, somewhat after the manner 

 in which the hepatic glycogen may be considered as stored car- 

 bohydrate to be delivered as the needs of the economy necessitates ; 

 if so the colloid material should show further evidences of change, 

 at least, under certain conditions. That the colloid does undergo 

 changes is evidenced by the appearance within its otherwise 

 homogeneous mass of such structural alterations as vacuolation, 

 basophile degeneration, and disintegration into granules of greater 

 or less size, changes which are frequently observed (figs. 14, 15 and 

 18). As to the physiological nature of these changes in colloid, 

 and their possible connection with a storage function I can offer 

 no conclusive proof, but it seems to me quite possible that such 

 a relation exists. 



The thyroid follicles are lined by a simple columnar type of 

 epithelium (fig. 11) whose cells show considerable variation in 

 height. In the same gland the epithelium lining certain vesicles 

 measured as much as .010 mm., others only .006 mm. The epi- 

 thelium of occasional vesicles was even lower, but was possibly 

 open to the criticism of mechanical distortion since the colloid 

 was often crowded against one side instead of lying in the middle 

 of the follicular lumen, even though the tissues had been prepared 

 with the greatest care. Being anxious to avoid any possible 

 distortion of the tissue, I removed nearly all of the glands 

 studied without allowing them to be touched by either instru- 

 ment or fingers, the knife or scissors being passed through the 

 muscle beneath, and the gland, supported on a thin layer of 

 muscle, dropped bodily into the killing fluid. 



As a rule those follicles which were well filled with colloid 

 possessed low epithelium, in those with taller epithelium the reverse 

 was the case. In making this comparison the surface area of the 

 sections of colloid mass was compared with that of the containing 

 follicle. The average height of the epithelium of a number of fol- 



