NORMAL MODE OF SECRETION IN THYROID GLAND 51 



It is necessary, however, under this hypothesis to explain the 

 occurrence of intrafollicular colloid, and its variabiUty in differ- 

 ent members of a species and under different experimental con- 

 ditions. In my recent studies on the changes in the hyperplastic 

 gland of the opossum and its changes under domestication, I have 

 shown that all the stored colloid may be withdrawn from the 

 gland in a short period, and that the gland will maintain for a 

 period of several months a condition in which little visible colloid 

 is present in the gland, but, as Marine previously demonstrated 

 in the dog, if iodine be administered the vesicles are reformed , and 

 filled with dense colloid. In the opossum this colloid makes its 

 appearance first deep in the thyroid cells, but migrates to the 

 free surface and is there discharged into the lumen. I have also 

 found in the study of many glands from cases of Basedow^'s dis- 

 ease that the few colloid droplets which are present are very fre- 

 quently found at the level of the nucleus, or even in the base of 

 the cell. These facts indicate that in addition to the direct 

 mode of secretion there is an indirect mode, which consists in the 

 condensation of the secretion into the form of droplets having a 

 high content of solids, and the extrusion of these droplets into the 

 follicular cavity. These droplets are formed in the same zone of 

 the cell as that in which the primary or direct secretion is formed, 

 and it is probable that they are formed at the expense of the 

 latter. 



The readiness with which the thyroid gland undergoes hyper- 

 plastic change, its responsiveness to iodine administration, as 

 demonstrated by Marine and his co-workers, the ease by which 

 it may be modified structurally by dietary conditions as shown by 

 the work of Reid Hunt (/ll). Marine, Chalmers Watson ('07), 

 Tanberg ('00), and MissiroK ('10) and confirmed by my recent 

 studies on the relation of diet to hyperplasia in opossums under 

 domestication, confirm the conclusion that there is a delicate ad- 

 justment between the functioning of the thyroid gland and general 

 body conditions, though at present we do not know the means 

 by which this adjustment is mediated. This being the case it 

 may be assumed that only when this adjustment is disturbed so 

 that the rate of secretion is in excess of bodv needs, the indirect 



