THE THYEOID GLAND AND ITS DISEASES 



215 



desquamated epithelial cells. Their remarkably close correspondence with 

 the individual vesicular cells (Fig. 5) indicates that, in some cases at 

 least, they are produced by the cells and represent a more fluid secretion. 

 The irregular notched border of the colloid substance, which is frequently 

 met with, is probably due to the shrinkage caused by fixation. Newly 

 secreted colloid is more fluid and stains less intensely than that of longer 

 standing, though some believe the reverse to be true. According to Gley, 

 a pilocarpin causes swelling of the thyroid and the collection of colloid 

 matter in the vesicles." It is also 

 claimed (Licini) that the colloid is in- 

 creased by removal of the pancreas, as 

 well as by thyroid feeding. 



It is generally admitted that the 

 colloid cells of Langendorff, which are 

 sometimes present, are undergoing de- 

 generation, being in the last stages of 

 cytomorpho'sis. The presence of two 

 distinct cell types, as discovered by 

 Bensley in the opossum and illus- 

 trated in Fig. 6, is interesting, since 

 it indicates the possibility of a plural 

 secretion. 



lodin Content of Colloid. The chief 

 characteristic of the colloid substance is 

 its iodin content, which varies in amount 

 with sex, season, age, and diet (McCar- 

 rison (&)).- Baumann's claim that giving 

 foods rich in iodin increases the per- 

 centage of iodin in the gland, remains 

 unconfirmed (Gley). In certain intox- 

 ications colloid with different staining reactions has been described. Vin- 

 cent claims that "iodin is absent from the thyroids of some animals" 

 and that it cannot always be -found in the human thyroid, and Schafer 

 seems to think that the autocoid is not necessarily iodin containing. 

 More recently, however, Kendall has isolated from the thyroid a crystalline 

 substance containing iodin, which possesses most striking physiological 

 properties. 



Colloid Resorption. Champy's experiments with tissue cultures of 

 the thyroid are of interest with regard to the normal mode of resorption 

 of the colloid. In his experiments he finds that it passes through the 

 follicular epithelial cells into the neighboring lymphatic spaces. Since 

 the resorption is nearly complete in twenty-four hours, he concludes that 

 it normally takes place quite rapidly in the organism. In his opinion, 

 the contents of the follicles are almost completely renewed every twenty- 



Fig. 5. Portion of wall of human 

 thyroid vesicle showing close asso- 

 ciation of clear droplets with indi- 

 vidual cells (magnification 900). 



