38 R. R. BENSLEY 



thyroid substances. Some observers have even doubted the 

 resorption of this material, and have suggested that the function 

 of the thyroid gland was primarily to withdraw toxic substances 

 from the blood. Others have conceived the colloid as a sort of 

 menstruum in which the real thyroid secretion was received and 

 from which it might be withdrawn without visible change in the 

 colloid itself. Still others have held the view that the colloid 

 was the real secretion of the thyroid gland and that the normal 

 mechanism of thyroid secretion was by this indirect route, first 

 secreting into the centre of the follicle, and then withdrawing 

 this ware-housed material, as functional needs required, by some 

 unknown method and route. 



The determination of the true significance of the colloid in the 

 secretory cycle of the gland, and of the ways in which it is formed, 

 and of its intracellular antecedents, is of fundamental importance 

 in the physiology and pathology of the thyroid gland. The con- 

 viction that it is by this indirect method that the thyroid gland 

 produces its internal secretion lies at the bottom of all of our 

 mare or less speculative interpretations of pathological conditions, 

 and in view of the strong physiological evidence supporting this 

 conviction few have had the courage to question its accuracy. 

 Many authors have tried nevertheless to influence experimentally 

 the rate of secretion in the gland, and to read in the changes so 

 produced the true history of its secretory process. In this way 

 many interesting facts have been discovered, which at present 

 seem to some extent contradictory of one another, but which 

 nevertheless must be found to be in accord when the true history 

 of the process is revealed. 



Our earliest knowledge as to the origin of the intrafoUicular 

 colloid of the thyroid gland is due to Biondi and Langendorff. 

 Biondi ('^w) showed that this substance was a true product of 

 the secretory activity of the thyroid epithelial cells, inasmuch 

 as he found globules of similarly staining substances in the cells 

 themselves. He conceived the process of secretion as follows: 

 the cells of the thyroid gland produce the colloid, since one can 

 see in them little globules having the same microchemical reac- 

 tions; the vesicle has a tendency to increase in size partly b}'' 



